I tried out 4 different more expensive "audiophile" power cords vs a heavy duty Belden 14ga, shielded cable which cost me around $12. Tried them in multiple systems, which included amps from Cary, Audio Research, Parasound, Bryston, and Krell. Preamps from Audio Research, Conrad Johnson, and BAT. I had 3 other people participate in the comparisons, including two audio store salesmen.
Cutting to the chase, none of us could detect any differences. I am still using the Beldens today. I'm not all that certain that they are any better than the stock power cords. I'm willing to spend more on power cords if I felt they made a difference, as I have spent many thousands on my audio system, but I've never heard one that convinced me it was worth the money.