Awesome. Now you've "improved" a 6 foot piece of power cable. What are you doing about the tens or hundreds of feet of cable in your walls?
My standard build procedure involves exactly 8 minutes of loving kindness meditation towards the gear I'm installing. It really* works.
I have also looked into and experimented with "the tens or hundreds of feet of cable in your walls" as well and have optimized and documented my results.
These results are posted in the Cookbook thread, to wit…
https://www.head-fi.org/threads/the-diyrs-cookbook.781268/page-43#post-12738982
and
https://www.head-fi.org/threads/the-diyrs-cookbook.781268/page-92#post-14746426
These 2 series of tests reveal what improvements can be made not only by power cables, but also what can be achieved by those "tens or hundreds of feet of cable in your walls".
And to a certain extent why there is any improvement, and certainly can be an answer that can be clearly understood.
TL;DR A critical factor in all of this is the ability of the ac power delivery system to supply BIG current to our audio gear in short dual ≈ 3ms pulses out of our 60Hz (US power) line voltage. This includes the outside step down transformer and the cabling that feeds our homes, along with the main breaker panel, the branch circuit we use to feed our audio gear, the duplex receptacles, our power cables, even the fuses that are inline with this delivery of power into our gear.
So yes I have looked into this, extensively, and documented the results and optimized the power delivery into my gear and have gained the subsequent improvements as a result.
And yes, that last 6' of cabling is but one aspect of the whole picture, and is one that I can and have made improvements to and it certainly can make a difference.
And of course YMMV.
JJ