After weeks of searching for a viable way to run a Mac on 208 vac, there seems to be a breakthrough.
Gadd, I hope no other Mac user has to go through this.
What a circus.
I am in the final stages of negotiating with a custom transformer builder for the step-down xfmr I need.
Gotta knock down my raw 250 vac to what the UPS needs, 208 vac input.
My UPS will grind out 208 vac to the Mac, with a beefy 13.0 amps rms behind that 208 vac.
The Mac Pro itself will only use 6.63 amps, but I have a bunch of big printers and other stuff that will use the rest of the 208 vac juice.
Most other custom xfmr builders wanted $2000, so I had to do a heck of a lot of shopping to get the price down to something semi-reasonable, in this case about $700. (negotiation still in progress on price)