Why do I need power management if I have a great power cord?

I guess, what I wonder, is if some “power conditioning” devices still may add value.

If passive devices, it can, and will be marginal.

I’m going to research more into the 240 V option that makes sense. Does anybody else know anything about this?

Yes. If you are having problems with AC line noise, this will do nothing since the noise is coming from outside the house. Your house is powered by 240V which is split into two halves; that's what electricians are talking about when they talk about 'the other side of the line'. You can see this by simply looking at your breaker box- the left and right columns of breakers are the two sides of the line. There is no transformer involved to cause the two sides to be 117V  (or 120V or whatever).

I learned this the hard way about 30 years ago. I built a loft apartment in an old building and when I put circuits in the panel I didn’t know about balancing the load. When I got my first electric bill it was sky high. I was delivering parts for an electrical construction company and I asked one of the engineers what happened. He Came over to inspect my job and laughed because I had all the circuits on one leg. He explained me that the electric meter reads the higher of the two legs and if you don’t balance the load you’ll get a crazy electric bill.

... I really didn’t sign on to audio Gon tonight looking for a beef. I guess some of you guys are hearing something, I tried to hear it and spent a bunch of money in the process and nothing...

Money that may have been better spent on things that do make a difference

My answer is yes to your first question, but your own conclusion is incorrect. It doesn’t require a detailed knowledge of logical and/or formal fallacies to understand why that may be so.

…

People often will spend a few hundred or more on questionable things, and do it multiple times. And often not spend teh same total amount in a single “upgrade”.
Hope rings eternal.

@atmasphere do you have experience with your amps benefiting from using the two example of power conditioning units that you mentioned?

@hilde45 +1.  And, thank you.

On my system power cables do make a difference with power conditioner or similar such devices. I use two WyWires Juice II Platinum HC power cables on my Nordost  QB4, one feeding the QB4 and off from that one feeding my amp. It clearly is noticeable changing out power cables. I’m evaluating at the moment a Nordost Valhalla II PC feeding my PS Audio P10 and it is noticeably different than the WyWires Juice II Silver HC I own and currently use. Dedicated circuits definitely make a difference as well, but system dependent. Before dedicated circuits my Pass X250 was a little on the lean side and lacked authority; adding dedicated circuits opened up the Pass and extended and controlled the bottom end. I ran No.10 to my amp and another No.12 circuit to the rest of my system. Best just to try for yourself and not be steered one way or another by others.