With my "Engineer" brain, I never believed any of this stuff about power cords sounding better/worse, or even different. Then, after chasing an intermittent problem/funny sound, for several months, in an Mc60, I became a believer. I had a cruddy power cord. Changing to a new "high current" cord, the problem immediately vanished and never returned in the 30 years I used that amp.
So yean. Power cords. Relevant.