@donavabdear , apologies for not ignoring the man child. I will try better.
Had heard a lot about the PS power plants, but never dug very far into them so read a bit and talked to one of my EEs. The PS units are not true isolated regens so that may be why they don't solve it. Odds are good that the extension cord is getting you onto the same phase as your other equipment. Shouldn't matter, if you can, plug everything into a single phase. Easiest way to test is plug everything into a single power bar. Just don't turn it loud and you should be able to test.
@invalid , a page or so back, I posted what Stereophile measured for SNR, 90db on balanced, but that pre-amp has really high output and they may have measured that 90db at the full output level. At a normal level, it could be 10-20db lower. That would be audible. The unbalanced are even noisier.