Upgrade Power cord on Plasma TV?

No and No. A good power conditioner/regulator might assist in the longevity of the plasma's power supply, but you will not see a difference unless you are already having an issue.

And here is some info on why it's not:

http://www.avsforum.com/avs-vb/showthread.php?t=694747

i'm using an interior extension cord for my wall mount pioneer. i'd like to get a longer cord to eliminate the extension. i've looked at the Volex website, but I have no idea what i need. i'm thinking polarized, but that's about as much as i know. what about the inline filter on the OEM cord? can someone point me in the right direction?

ABSOLUTELY POSITIVELY NO IN BOTH CASES. This is one of the biggest snake oil ploys in audio that I guess is creeping into video. Use that money your were going to waste for a nice dinner at a fancy restaurant

I can second (or third) that. I bought (with a full refund guarantee if not satisfied) a beautiful $400 braided power cord that was as thick as a garden hose. The guy in the A\\V shop said it would produce a noticeable improvement. I was actually pretty excited about it - until I actually hooked it up. Swapped it in and out with the stock cord dozens of times over three days - NO DIFFERENCE. Went back to the store and they happily refunded my money.

Hope you're not putting that cord inside the wall... here's why you should NOT conceal any power/estension cord in the wall or ceiling. FAQ click here why not.

try it and see. i doubt it, but who knows.