How can I put this delicately (and I mean no offense)? Are you new to the audio scene? There's an immense amount of information out there on this particular subject. All you have to do is search for it.
A lot of that information is largely marketing.
There are power cords out there that go for thousands and thousands of $$, and audiophiles swear by their performance.
They do indeed swear by it.
Right. But where is the evidence that technology, and thus, performance, has advanced in the last 5 years?
Largely there is not any. There are a few papers on power cords.
… And some power conditioners show suppression of AC harmonics.
But there is also the other snake head on the hydra, where we do not know which amps have power supplies that are more immune to noise than others.
It could be true that some power cords help some amps. But with N amps and M power cords, it is an NxM solution space… and add in power conditioners and it becomes an even more massive set of combinations.
I’m not talking about price. I’ve been at this for 40 years, so I’m no novice. I’m also a rational thinking person
You may not be the audience that the power cord people are catering to.
… that needs to see some concrete evidence to substantiate such absurd claims. No need to be delicate. Just show me the empirical evidence. Simple.
Sadly you will probably be disappointed, as the examples seem well hidden to my searches.
But a lot of people that I loosely know, and also respect, seem to also swear by cables, power conditioners and a lot of high-end ICs and speaker cables.