I wonder why......

If power cables offer such dramatic improvements (not saying they do or don't), why don't component manufacturers supply them as part of a component sale? All high end components come with power cords that can be disconnected. The cost of a mid level aftermarket replacement cord is only a fraction of what the typical high end component costs so if sound is improved so much, why wouldn't a manufacturer want to "improve" the sound of their components by providing an upgraded cord at the point of sale? 

High end automobiles (Porsche, Ferrari, AMG, etc.) are typically supplied with the best tires available on the market. Often these are specifically designed by tire makers to the auto maker's specs. This is to extract every ounce of performance from their product. If high car makers did what audio manufacturers did, they would be supplying their cars with average, run of the mill tires expecting the buyer to upgrade on his own. Wouldn't audio component makers want to extract the best performance from their gear?

The only thing I can think of is that audio component manufacturers don't think so called upgraded power cables are worth the added cost.

What am I missing?

Oh, geez, here we go again! 😬
The short answer is because each buyer has a unique preference on how to further fine tune the components in his/her system.After market cords all have  different 'flavors'.
well you didn’t miss an opportunity for some trolling.

What have your experiences been with different power cords (not saying you did or didn’t)?
What lengths should they make? Then they have to design and build the cables when they are not cable makers. Then they have to charge for it? Adds cost to an already high priced product!  Then we Aphiles will say we prefer the one we have or another etc...and want to return it.  The cable business is not easy.  Just a couple of reasons. Many more. 
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The manufacturers do not supply high end cords because it would take sales away from the cable company’s. Plus, if you are going back to the audio store to buy cables, you may see something else from your amp/preamp/front end component manufacturer that you might buy in the future. It is to get you back to buy more and more audio equipment.

I am in the camp that I will not spend over $500 on a cable and I prefer to buy them used. All my power cords are Shunyata and I haven’t spent more than $300 on any of them and most retailed for over $500.00. When I see someone with a 5K system, talking about buying a 1K cable, I ask...…..why?
No matter what high end power cord the manufacturer provided audiophiles would complain and replace it with a different high end power cord. The smart thing to do would be to not (rpt not) include any power cord and knock a few bucks off the price.
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Stock power cords are great for initial burn-in. Another use for them would be to include it in the resale for cable naysayers 😉

I won’t go into the merits of aftermarket PC’s....if you hear the difference, great. If you don’t, enjoy the stock cord.
What am I missing?

The will to search the site and read. : ) 
The people who care will want to choose their own cord.   Pretty simple.
This could apply to any component of any piece of audio gear. Let’s not stop at power cords. Why don’t they use upgraded tubes instead of mainly EH? Why not upgraded caps? Binding posts? Heck, if the manufacturers understand the synergy so well they might as well give you the best ICs and speaker cables while they are at it to properly match their gear. droning sound...…………….
If the stock cords sound as good as the big dollar ones, then I am sitting on a gold mine! Have to go now and list some nice power cords....
Most electronic manufacturers just don't buy into the extreme hype about power cords.  At the same time many if not most audiophiles do.  The compromise is the IEC spec inlet.  There was a time when high end equipment came with non-removable power cords.  But that was back in the days when Patti Page was on the radio.
It's because electronics manufacturers tend to know how electronics work, unlike most audiophiles. 
Silly question. The stock factory power cords are there so when you sell you can keep the good one you bought and the other guy still has something to plug it in with. Duh.
Everybody loves options.  Separating cable purchases from components offers endless options to the audiophile.
If you have a choice between two $3,000 amplifiers but one comes with a boutique cord that adds an additional thousand to the price...

No manufacturer wants to price himself out of a sale or have to sing the praises of a brand of power cord to make that sale.
"If power cables offer such dramatic improvements (not saying they do or don't), why don't component manufacturers supply them as part of a component sale?"

They do supply them... (they just sound bad)
... jchiappinelli:  regarding tires on high end cars: they cover themselves legally by specifying and supplying specific tires. The car owner always has the option to change but the car is tested and documented with specific tires, solely for legal protection of the company.
Lol boxer!! OP what do you think about wall warts?
The bog standard power cables that come with your gear meet code, and that's about it. 
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Re: Supercars, they still don't use the best wheels and tires.Not Carbon fiber for the lightest, not slicks for the best traction... But perhaps it's good enough to drive to the grocery and back.
Be fun to A/B test cords blindly on an “audiophile “ . Like myth busters. I’ve had cord salesmen tell me theyve heard systems with various cords that repelled them and that they had to leave the room . . If only they would spend half as much on a shrink as they do on pricey wires. 
Take a look at an amplifiers fuse. Stare at that tiny wire inside. All your power goes through that tiny little wire. 

Take a look at the main power transformer in an amp. Regular copper wire, no upooc, no single crystal, no 6nines, 16awg, 18awg, 20awg? All your power goes through that 'awful' transformer.

Take a look inside any high end phono preamp. Not a single piece of multitrand, anywhere. The exception is Litz wire.

My wife has enough shoes and jewelry for 5 wives, she still buys more. A cousin has 50+ watches, he still buys more. A friend has a dozen vintage cars, he still wants more. I have 3000+ albums, I just ordered more.

What am I babbling on about? We buy because we want to buy. We hear a difference because we want to hear a difference. We justify our purchases because it makes us feel better. If you have the means, you justify the end. Money makes the world go round. Keep spending!!!
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I just replaced a customer's stock power cord on a $25k amplifier with a $3k Shunyata Sigma. The difference was immediate and obvious. A few hours later the customer called me to tell me how happy he was, how much he was enjoying his music. When he bought the amp a few years ago he was given a choice, and claimed he couldn't hear a difference between the stock power cable and a then top of the line power cable. In the interim, he upgraded his speakers to Wilson Sasha DAWs, his DAC to a Berkeley Reference DAC, added a DCS Network bridge to feed the DAC, and upgraded from a Mark Levinson to an Ayre preamp. My point is first that his system now has sufficient resolution to appreciate the improvement provided by the new power cord. Second, manufacturers of cables continue to learn how to make their products better.
Finally, it would be unfortunate not to get as much performance as possible from one's investment in components!
It is not at all obvious to me that experience in designing and manufacturing exceptional amplifiers (for example) gives a company a leg up in designing cables.
In fact, one of the very best manufacturers of high performance amplifiers, Spectral, depends on another specialist (MIT) to complete their designs.
To the OP; just try. I never built better systems until I started trying things out for myself. :)
I used to have a friend that enjoyed audio as much as I did. The problem with him was that he didn't want to spend any more than what he thought he should pay.

He was always jealous and could hear the difference but over time he rationalized his point of view to the extent that he would intentionally get into arguments with salon owners, confronting them on the cost.

He would listen to any new piece of gear I bought and just stand there, getting upset and trying his best not to show it, but his facial expressions and body language betrayed his feelings. Jealousy. Pure and simple.

He could hear the differences but outright dismissed them as not important enough to justify the cost. His only joy was to play it as loud as he could and grin and smirk about it, as if he achieved something.

That is what I hear when people deride and decry such things as the efficacy of aftermarket power cords, or anything, for that matter. The put on a show, portraying themselves as out to save you from yourself. 

All the best,
The comparison to high end tires is weak. Tires are easily tested for speed, control, and tread life. Its easy to test tires on a track and pick out good performance tires vs stock Ford Fiesta tires. To me, that's where making statements like "a huge difference" is valid. Audiophiles are constantly preaching  to the enlightened choir because the average music lover will never understand what they are not hearing. Sad.
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Nonoise, your friend reminds me a lot of this one audiophile I used to know. He couldn’t go two words about wire without turning it into some kind of rant or snide comment. Or for sure the eye roll or like you said, facial expressions and body language giving the truth away so no matter what he said you just knew he was convinced its all BS. Which I wish I had on video the time he brought his masterpiece homebrew wire over to demo, only to hear with his own ears just how pathetically awful it was. I mean there was no denying it. And he knew it. No matter what he said, the truth was as plain as the pain on his face.

This is what I really do not get. If you can’t hear a difference, why not just say you can’t hear a difference? Totally understandable. We all start from zero. Or if you can hear a difference but its not enough to be worth it to you, if you value your money more highly than your sound, why not just say so? Isn’t this the very basis on which to build a system? By putting together a bunch of components each of which are deemed the best value at the time? "Not worth it" is in that sense positive. Progress. Essential, even.

To be in denial though, that I do not understand at all.

The year is 2019. Four years ago Ted Denney came out with the 20th Anniversary Edition of his AC Master Coupler. 20th anniversary. Plus 4 years. According to my math that is 24 years. And Synergistic Research was hardly the first. They just happened to be the one to come out with a power cord so freaking good it sold for over 20 years and still commands high resale value even now.

That is an awful long time for there to still be people around so obtuse they still don’t get it. I mean that is the kind of dense known to warp space and time itself.

I've always wondered why there is a difference with a couple feet of power cord when there is literally thousands of feet-miles of wire between your power generator and your equipment. lets not even get into the wire in your house or what's inside your equipment i.e. transformers - hook up wire. . So why does that  few feet make a difference? I hear it and I'm still baffled by it. Why would direction make any difference in a power cord it is AC power after all. 

Maybe its real maybe its hopeful thinking but dam if I don't have an aftermarket power cord on everything..... sucker maybe, maybe not...but I'm not complaining when I'm sucked into my chair listening to music. 

After all its all about the music right? RIGHT!
Couple of comments;

1. Never said aftermarket power chords didn't have an effect or weren't worth it. Just raised a question about why they weren't offered as part of the OE package. Raising the thought that perhaps OEMs didn't feel it was worth it was not a condemnation of those who buy and claim benefits from aftermarket cords. I haven't had that experience thus far.

2) Responses fall into the usual 3 categories; 1) those that address the question and offer constructive commentary, 2) those that miss the point of the question, and 3) those that have no idea what they're talking about.

3) Constructive responses (IMO) that I hadn't considered included granny ring's "what length?", millercarbon's "needed for component resale", and pgaulk60's " everyone loves options". All good points.

4) Several responses supported the "there is no point to aftermarket cords" theory.  Whether true or not, that was not the point of my original question.

4) Several responses supported the "there is no point to aftermarket cords" theory.  Whether true or not, that was not the point of my original question.
It happens all the time here. 

4) Several responses supported the "there is no point to aftermarket cords" theory. Whether true or not, that was not the point of my original question.
That may not be the point of your question, however, it doesn’t change the fact that it’s the truth.

There is no scientific evidence whatsoever, that backs up the claims of cable manufacturers, least of all the sort of claims we see from the likes of Synergistic Research.

For those who like the flat-earther analogy, you might as well ask why globe manufacturers don’t make them flat (well, there are one or two knuckleheads making them). And to answer as to why we should care, it’s because the perpetuation of pseudoscience in this country is leading to a state of regression.
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My take on all of this is marginal cost, marginal gain.  I am married to an Ivy PhD economist who supports my music jones.

When you maximize your speakers, amp, preamp and source, the natural next step is power conditioners, power cords, etc.

At that point they have maximum value, before that not so much.  

I would also add room treatment comes before these items as well.  It is all part of a natural progression forward.

Aficionados of items beyond basic components typically over value their favorite, but they all have value.  Again, marginal cost versus marginal gain is my mantra.

There is room for all here
Has anyone asked amplifier etc. manufacturers? Maybe they know the answer.
That's been gone over before. Some say no, some say yes, by all means, try an aftermarket PC. One that comes to mind is Kinki Studio. 
Under the heading, UNPACKING, they state:
-El Cheapo Power Cord (Please use your own audiophile power cord for best sound).

All the best,
Why does the sun go on shining?
Why does the sea rush to shore?
Don’t they know it’s The End of the World

[Verse 2]
Why do the birds go on singing?
Why do the stars glow above?
Don’t they know it’s The End of the World
 I know many folks don't care for blind testing. However, why not use it as just a part of your buying decision? Get someone to plug in 1 cable (or any other power conditioner), listen to it for 1/2 day, do the other next. If the difference is huge, (as claimed by some) say, like the difference between a cheap speaker and a well reviewed audiophile speaker, you may only need a minute or so to discern the the difference. If the difference is subtle it may be still very worthwhile to add to your system. I keep hearing "trust your ears" not only the specs. I know there are variables in a/b switching but I would think a cable would be pretty straight forward. And who cares about the variables? Just pick the one that sounds better. I would also suggest a significant other to monitor the trial. This would substantiate the results and give you leverage to spend the extra money. 
The thing you are missing is the human desire to accessorize, and the dealer's markup on them.

Selling a dress is profitable, but the purse, shoes and belt will double the dealer's profit.

High end watches may be sold with very nice straps, and yet still the buyers want to get something different.

I know many folks don't care for blind testing. However, why not use it as just a part of your buying decision?
Some have done just that.
Have you? If so, how did you conduct the tests? What were the results?
jchiappinelli -You're not missing anything, but you knew that before asking the question, didn't you?