Best Powercord for a TV?

Hello everyone,

So my question is whats a good powercord for a tv? I recently upgraded my LCD TV and plasma tv with Richard gray powercords and they actually made the picture worse compared to the stock cord.

I had a ps audio powercord and a old transparent cable powercord that I tried as well and although they where better than the Richard gray, the picture quality was not that good.

For some reason the powercords made the black color look weak and choppy.

Are newer tvs made differently than older ones? I remember upgrading my plasma tv years ago with a transparent powercord and it made one hell of a difference.
Any suggestions?