I would simply like to see a waveform analysis of the power, going in and coming out. Forget FFT and so on--just show me the waveform on a scope for starters. If that looks bad, then okay. If not, then let's do a spectrogram and see where the noise is. Then, let's see if any of that noise is coming out of any of our audio equipment. My bet is 1.) power line noise is negligible most of the time, and 2.) the filter caps on the power supplies of my equipment clean it off if it isn't.
The only power regenerator I know of that will remove noise better than the noise remover of a good power supply (which most good audio equipment already has) uses inertial mass--incoming power spins a flywheel, which drives a generator for outgoing power. That's "regeneration". And if the flywheels is heavy enough, it will cover over dropouts very nicely. And it's a great surge protector, too. Granted, it's acoustically noisy and the size of a lawnmower.
I use a more sophisticated power supply for my Thorens turntable than the 16VAC wall-wart that came with it. The one I use was made by Music Hall, and on ebay I paid a little over a hundred for it. I haven't hooked up a scope, but I really should. The main advantage, though, is that it will drive the synchronous motor in the Thorens at any speed, so I leave the belt on the 45RPM part of the pulley (which is larger, so less slippage and belt hysteresis, and less dependence on the kludgy belt derailleur for changing speeds), and can also make fine adjustments to speed to match pitch. Sometimes, I play along to recorded music, and LP's are often cut fast to get a bit more music on a side. Those are features worth a C-note or two to me. But I'll bet the AC waveform coming out of the Music Hall isn't any cleaner than the one coming out of the wall. In fact, I would not be surprised if the AC oscillator is digitally contrived and rather steppy.
If someone wants to put ferrite beads on their AC cable to choke common-mode RF, fine. Those are not expensive. It's not impossible for power lines to pick up RF in an RF-rich environment. I think I induce a little RF in my power lines when I press the talk button on my kilowatt ham radio transmitter, because I'm using a tuning network inside the house to match the antenna for some bands. (Not that I use the power most of the time--usually the 100 watts out of the bare radio is more than enough for my purposes.) Does that happen in New York apartment buildings? Maybe--people use their AC lines to carry "smart home" stuff and even Ethernet signals, but I'll bet not a bit of that makes it through even cheap power supplies on our systems.
How hard would it be to show O-scope traces or FFT spectrograms of the power going in and out of these devices? I'll bet that Mr. Fremer has the equipment to do that in his apartment already. Maybe not. If they are the same, then perhaps he would be willing to test his perceptions by a simple blind test. Blind testing of some things requires a lot of apparatus and time, but not this, it seems to me.
I do note that in one of his videos, he claimed off-handedly to hear the effects of crystals placed here and there (I suppose according to a plan). If he hears it, well, fine. I'm glad my hearing is unsophisticated enough not to need such self-delusions enhancements.
Rick "where is that oscilloscope? Oh, there it is..." Denney