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

Still waiting. See I'm one of those guys who actually took a physics class, studied power distribution and networking, and practiced it professionally for nearly 50 years, and have seen and heard, if not all, most of the tweaks in that time.

Here's one - the original Monster Cable demo had 18 Ga lamp wire rolled in a coil behind the switch while the Monster Cable was laid straight. No surprise the Monster Cable A/B'd better - the coiled lamp cord was a series inductor, AKA a low-pass filter with measurable DC resistance. Trim that out and the difference went to zero. 

If a power cable 'lowers the noise floor', that would be measurable, and might just help things.  Anybody ever measure that? Yeah, didn't think so. 

@jacobsdad2000 zzzzzzz ? Yeah, that would be a grounding issue. As in your lack of grounding in basic physics and electronics.

@h4k4lugi Thanks for posting that. I have no doubt bringing in Shunyata to design and implement a fully developed and integrated power, grounding, and interconnect strategy can yield a 10dB improvement in a studio. But that is a very different thing than swapping just a power cable at home. 

One of my jobs along the way was developing grounding and cabling schemes for large live sound touring systems because having to pick up and move several semis of gear every night then rebuild it in a new venue, with new power on a tight timeline is a huge challenge. And 10dB can make the difference between a great show and an unhappy band. But the key point is that it takes an understanding of the entire system requirements and a whole system solution. There are no single silver bullets. 

@ditusa Hope you never have a fire, because if you do you won't get dime one of insurance. What you've done is a complete violation of the National Electrical Code, and an adjuster will notice it in a heartbeat.