Having owned a Pass Labs Aleph 3, I recall reading something in the owners manual that due to its design, aftermarket power cords would not yield any affect. I found on that amp Nelson Pass was correct, as an NBS Dragon Fly made no audible difference on the Aleph 3. So I put the cord on my DAC where I could hear a difference.
So given the controversy of the subject, perhaps there is something to be said that maybe the whole issue depends on the component...