AC captive cords???

How about changing the sub over to an IEC type connector.
The 1st time I changed some captive cords with better quality power wire, I wasn't elated with the result.
Made cord comparisions length changes easier too.

parts express IEC's

Carefully wrap the cord with twenty dollar bills. Be sure to use cryo-treated scotch tape to hold them in place. For even better results, try fifty dollar bills.

If it's a newer model sub with a captive cord, it's probably not going to benefit from a more expensive/better PC, or the manufacturer would have made the stock cord detachable to give you (and the sub) that option.

On the other hand, if it's an older, but very high end sub like an Entec, or an early M&K or Velodyne, you could try it, it might improve the performance a bit. But I wouldn't recommend the Mapleshade method -- to many electrical interfaces, defeats the purpose IMO. Either hardwire in a new and better PC, or have a tech install a male IEC panel connector on the sub so you can try a number of different PCs.

Eldartford,

It's important to note that the bills must be the older, 'uncolored' versions. The dyes in the newer bills increase dielectric absorption, and will result in significant coloration in the upper to upper-upper googlehertz region. Of course it can be difficult to hear the difference if your system isn't tweaked properly. I find isolating my loudspeakers from the floor with short stacks of 100 dollar bills really increases the dynamic slam and midrange bloom, especially when listening to vinyl that has been properly 'burned in' by repeated playing for a minimum of 25 years.
As always, YMMV.

(Thanks for letting me play, I needed a good chuckle today)

Thanks for the response all, i'll have to think about my options... Eldartford and Tplavas, are you guys sure your not rolling up those bills for other things beside audio???(:^)----

just for kicks and giggles, you might try an "after" line cord. get an adapter and connect another line cord to the captive line cord. assume you have a spare line cord, the cost of the adapter should be about $25.00 .

Although it was for a captive power cord on a Cary SLA-70Sig tube amp driving a full range speaker with transmission line bass down to upper 20's (perhaps, not as deep as a true sub-woofer), the plugging of the captive power cord into the very highest version of the Mapleshade Records power strip (conditions without the appearance of being a conditioner) allowed the deep bass to become more defined, pitch accurate, and even deeper, by judgement of three pairs of ears (not confined to one head, by the way :>)
Not sure if this is an item with a return option, if you are not similarly rewarded by low bass satisfaction.
I would hesitate to clip short a captive power cord in order to attach the Mapleshade Records Pig Tail power cord option, although it is supposed to work, according to the website. It just seems so irreversible if you don't hear an improvement. By contrast, the power strip helps the sound of all component power cords that I have inserted, without any surgery.

Eldee: Applying money directly to the system, I love it! Cuts out so many tedious intermediate steps. Makes liquidity of the other kind easy too, but if it got out of hand it could put Audiogon out of business. Obviously higher denominations will sound best as you say, the ultra-high-end of course being OOP, NOS notes. Silver and gold certificates beat regular currency, with the $100,000 gold certificate the king of the hill...

Um, just to be clear, I was just having some fun with what Eldartford said. Sometimes we need a laugh in this 'serious' hobby. I'm a firm believer in power cables. For a serious answer to the original question, I had a similar issue with the captive power cords on the Marantz MA700 mono amps I use to drive the subs in my HT rig. I replaced them with cryo'd CDA 101 copper wire of 13 gauge net, and I did notice a small improvement in lower-bass punch. Of course the original factory captive cord was only 16 awg, so that probably explains most of the difference.

Tplavas...It's too bad when we can't laugh at ourselves!

hey guys, no offense taken, its all about having fun and not taking things to serious, i try to take my chill pill on a daily basis... :^)

For captive cords the Highwire Wirewrap works.

Try one of ZCable's Zsleeves over it.

I find a better cord results in tighter bass on a lot of subwoofers, even REL.

The captive cord is not because the manufacturer thought it was better. It was just cheaper for them to make.