There's a logical fallacy here--that what makes quality is the distortion of the audio amplifier. We don't know if those poor devices had good or bad power supplies, but we are pretty sure they had good power supplies, with respect to their ability to address dirty power, because dirty power didn't affect them.
So, the question isn't "do these devices help?", the question is "are there devices that depend on good power supplies to work well and don't have them?" That question was not explored by Amir's choices.
I agree with Amir as far as busting the myth that all devices benefit from cleaner power (as if they have no ability to do their own cleaning), and that is indeed the myth that is behind the sale of many such devices. But I also agree with John that the test does not support the categorical conclusion that external power conditioners are always a waste of money, because they certainly do solve specific problems in specific cases for reasons that can most definitely be described and measured.
Rick "who has actually looked at the waveform of a Music Hall Cruise Control on a scope, and found it to be quite smooth--a visibly better waveform than Amir's wall power--but who uses it only to provide adjustable turntable speed control" Denney