If we’re looking for lab tests, after searching, I can’t really find any. I thought for sure there would be at least one or two out there, but as of yet, I haven’t found one. It looks the only tests out there (beside manufacturer’s descriptions) are mainly from audiophiles who have bought these cables, and have provided there own personal listening evaluations.
It’s true that the vast majority of evidence supporting the claim that power cords can indeed impact sound quality is anecdotal. However, I would argue that the combined weight of such evidence is far too great to dismiss with the wave of a hand. I simply don’t find it credible that such a meaningful percentage of audiophiles are all slaves to propaganda and various, related biases.
Furthermore, there are individual examples that carry much greater weight than the average testimonial. Take, for example, Paul McGowan of PS Audio. He is a well-known figure, who has produced many, many videos in which he attempts to answer questions from audiophiles, and his company is well respected, from what I can gather.
So this relatively public figure, who certainly knows a fair bit about audio engineering, was for years selling power cords produced by his own company, but found that the high-end offerings of another brand (Audioquest) were superior, and not only decided to use them in his company’s extremely expensive reference system, but also to sell them through their website.
In the video (linked below), Paul says:
"we put every ounce of engineering knowledge that we had into [the PS Audio AC12] cables"
"Holy crap! It was so obvious...the Dragon cable blew away our AC12 – just blew it away. I wish that wasn’t true"
He also claims to have done A/B blind testing, and that "everyone" hears the differences. He challenges anyone who is skeptical of different power cables making a difference to come and listen.
The video is only ~six minutes:
To be clear, I have never used Audioquest cables, but even though Paul himself is unable to explain why there are such differences, it strains credulity to believe that he, and the others who were exposed to such tests on the reference system, somehow suffered from mass delusions.
This also touches on what I have argued for years, based on my personal experiences, and those of more than a few other audiophiles. If confirmation/expectation biases are the explanation for why people hear differences in cables, then how is it possible that some have, at least at times, had precisely the opposite experience? In other words, like Paul in the above example, I have had several experiences over decades of developing systems in which I was disappointed in a newly acquired component, despite having had great incentive to prefer it.
That doesn’t mean that I have "golden ears", nor that I never suffer from such biases. But it certainly does illustrate that hearing differences in cables can be the result of relatively objective listening.
As a final note, Paul does stress that his impressions of the cables were confined to their synergy with very specific PS Audio components, and within that system. And I agree that context and synergy are crucial.