Newbee,
I'll agree with Tvad, the power supply of a component won't prohibit if from being affected by it's power cord, although it does have some effect IME. I've had components with 2Kva transformers that were practically 'transparent' to sonic signatures of PC's, and mass-market stuff that only likes the cheapie PC that came in it's box.
In the very first iteration of my system, I tried a couple of PC's (TARA labs and Virtual Dynamics) and didn't hear enough of a difference to convince me I was hearing anything at all. The biggest sonic difference between that system and my current setup is the quality of the bass and mid-bass, and the quality and quantity of midrange dynamics. That early setup was pretty poor at differentiating bass notes, and most of it's dynamics were heard as upper-midrange harmonics, focused on the leading edges of notes, and weak on the follow-up. My current setup is better in all those respects, before any AC 'enhancements' are employed, and far, far, better after.