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

Synergistic Research A/C Master Coupler. Still have it on my Diablo 300.

For me it was a Cerious Technology cord one of the early ones I forget the exact model.

I acquired two Zu Mother power cords for my Shanling EL34 based monoblocks years ago and the improvement over the original factory cords was audible. I have never forgiven Zu… 🤣

@curiousjim I can think of only 3 possibilities.  

1.  your amp has a power supply that stores power for dynamics and bass in capacitors, chokes or other passive devices so tthat a large power cord isn't needed.  this is most likely.

2.  you're listening isn't good.  Not likely.  You're a veteran.

3.  your system sucks so bad it doesn't help  also extremely unlikely.

If you have a power problem with your amp, it will be immediately obvious when you install a $30 10awg power cable from ebay.

Now other components, such as DACs and streamers, have such minor power needs that it isn't unusual for a power cord upgrade not to change anything.

Jerry

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