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

I heard a difference with Shunyata Venom 10 NR - I acquired it for $350 as a demo.  I was 'lent' it to see if I noticed and appreciated the difference - it did and for me it was worth the price.

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