Jeff_jones, I found that difference between power cords on a certain component depends on several things. Just to name a few:
1) the overall resolution of the system
2) the quality of power supply in a given component.
3) room acoustics(which also contributes to bullet #1)
also, just how much different a given power cord will sound from a stock cord on a given component also depends on what aftermarket power cord are we talking about.
Example: you will hear bigger improvement over a stock cord with, let's say, a Shunyata Anaconda Helix, than you would by comparing the stock cord to Zu Bok.
Difference between power cords could be as obvious as between interconnects. Things like bass, midrange, instrument separation, air, soundstage, are all affected by cables, including power cords. Also, effect of power cords is cumulative. If you change one, you get certain amount of improvement(with the right cord that is). If you upgrade all, you gain more. Same as with interconnects.
This has been my experience in my system. As we like to say here on the 'gon, YMMV.