To, er, "contribute," we recently had a discussion about "power regeneration" for the smaller AC-powered products (you know, Magni, Modi Uber, stuff that uses wall-warts.) It's technically feasible to do something like feed a 60Hz sinewave into a Jotunheim and use it to output a perfect 60 Hz, 14VAC wave to power our smaller products.
And yeah, sure, youbetcha that this $399 cluster**** will make your $99 amp sound better. Or at least that's what some would say.
Hell, you could even use different AC frequencies to see if that made it better. And different output levels. I could look forward to emails about how 16.34VAC at 75.64Hz produces the most sublime sound from Magni 3. I could also look forward to emails about how using Mjolnir as an AC regenerator sounded even better, especially when using adapters and WE396A tubes. And, of course, the emails about how using a Vidar for each product in a stack (say, Eitr, Magni 3, and Modi Multibit, with 3 bridged mono Vidars--no big deal, just a $2100 power supply, right?)
(For those of you with a technical bent wondering about the math behind this, consider that V(p-p) = 2.83Vrms. So, if you want to swing 14VAC, you need about 40V of output swing. That's why you'd need something bigger than Magni 3--it only has 17V rails. If you want to swing 115VAC, you're looking at 325V output swing. That's a BIGGGGGG amplifier, with 170-ish volt rails minimum, plus tons of paralleled output devices if you want it to do 1KW continuously. Unless you're going Class D. Which would be a fine application for this technology, given good filtering. That is, if something inexpensive, convenient, and sonically transparent like the ugly-ass AcuPwr transformers didn't exist—and go up to 5kW.)
Or, to clarify: please DON'T do this. Get a step-up or step-down transformer if you need it, and call it a day.