One would think that they could put a scope (or A2D) on the power coming out the end of that cord… and then actually see some things that are other than 60 Hz (or 50Hz) being removed.
If I was able to see some high frequency noise on the bad cords, that was removed on the good cords, then it would be easier to imagine that that is a reason to believe in using a fancy power cable being worth having.
This post won the award for the most simpleton-minded.