What was the first power cable that you noticed a difference in the sound?

The first power cord that made a significant improvement for me is the Shunyata Venom V10 NR.  To my ears, it sounds best on my DAC.  A few years later I purchased a Shunyata Delta  V2 NR. Wow, that was an even greater improvement in clarity and  realism. I also use Shunyata Venom Digital power cords on my iMac and DDC.  Happy listening!

"If you heard any difference between a standard 12AWG power cable and a $500 Audio-Woo-Woo cable, it was confirmation bias or just delusion."

- Well, that clears it up, never heard that point of view before 🙄

+1 dill...I prefer delusion, as confirmation bias, even if correctly used, goes both ways...though I did buy the Woo Hoo not the Woo Woo

Unfortunately never actually, maybe I thought so initially, but I was skeptical of the placebo effect. I’ve owned Nordost, Pangea, Shunyata, Wireworld. I am currently running aftermarket Cullen cables. They are very well-made, reasonably priced, but I’m not sure if they make an actual sonic difference in my system. 

None!