I am the one who heard Kas’ Bryston amp performance with PS Audio Plus cable.
I have heard his amp many times before with previous power cord, and introduction of PS Audio did make noticeable positive improvement, no need for A/B testing.
I never liked Bryston amplification, sounds artificial, control and speed are there, but there is something metal and synthetic in the sound.
With PS Audio cable his Bryston amp sounded more natural.
Besides what Kas mentioned (soundstage and punch), there was improvement in timbre. For example, when drum is struck, you get a sense of membrane material, there isn’t only the main tone (thump) but more easily heard tones (harmonics) that characterize the material.
String instruments sound more natural, you can sense bow and strings.
Cymbals are not just annoying sizzling sound, but more real lifelike sound.
All this for some mean nothing or subtle changes not worth the money. For me, it made Bryston sound more pleasurable and natural, and that in my opinion is an enormous improvement.
I could listen for a long time to Bryston with PS Audio power cord, never without it.
So in my opinion Bryston owners would be well advised to upgrade power cords.
And it is not only about gauge. I will not get into the discussion about construction, choice of materials, etc., it will suffice to say that it is a mistake to assume the gauge is the only and the most important factor that determines the sound characteristics of cables, be that PC, IC or speaker cable.