AC captive cords???

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.

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.

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)