I have some upgraded power cords going to my amp and CD player. I never could hear the difference, but I had them around so I use them. Most of my system is plugged into an old Monster AVS 2000 Transformer. I have no idea how much that helps make my system sound better. I bought it many years ago and did A/B tests then, but have forgotten the results. (So, they didn't realy matter that much.)
My amp is plugged into the wall, as advised by people who say amps need to draw a lot of power sometimes and transformers and such can act as a bottleneck when the amp needs that rush of power. Good amps have internal power supplies, however, where they store the power they need.
So, I don't exactly understand what an expensive power cord buys you. Yes, I can see that it would provide cleaner power through better metals, but the power is going to get stored inside the amps power supply. Will the amp really know if that power came through a better pipe? Isn't it all just power once it enters an amps power supply?
Forgive my ignorance of electronics.