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

My first "contact" with the power cord issue was buying a high power Classe amp, 25 years ago, and one of the first things in the manual was the suggestion I should purchase an upgrade power cord...I was quite angry seeing this...bought an A/C Mater Coupler a few years later, and it did sound better...and the Classe included cord was a quality cord, not a throw away...sold the A/C coupler 10 years later, for the original used price I had paid...

Synergistic A/C Master coupler, long long ago....then Tekline, then Cerious Technologies...I also use the lower cost Transparent and Audience in secondary systems...found all worthwhile, and used power cords hold their value extremely well

I heard it immediately, as did a non audiophile music loving friend...and I didn’t want to like them, as I preferred not to purchase them...currently using Cerious Lumniscate in main system, and Cerious GE, Audience F3 and a low end Transparent Audio in various systems....using the old Tekline still in home theater...I sold the A/C Master 10 years after I bought it, for same price I paid...

what am I looking up at carpathian?

More than one high end electronics manufacturer has said they know most customers will buy the power cord of their choice, so no reason to add cost by including an expensive cord. Though some manufacturers like Pass and Rowland do include a "good" power cord (for their customers who will not buy an aftermarket cord, beats including a junk cord)...though they certainly use expensive cords at audio shows, and many seem to have a preferred brand...

+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