800 amps at 480 volts is certainly enough for a 12-stall (6 cabinets) Supercharging site.
Springfield, VA has a 1,000 kVA transformer for 18 stalls (9 cabinets). At full tilt, that's 111 kW available for each Supercharger cabinet. I'd have to go back and look, but I suspect the site was permitted at 1,200 amps.
800 amps @ 480 volts is 665 kVA, which we would round up to a 750 kVA transformer. At 665 kVA, that's 111 kW per cabinet at full load, which is right on the money.
Edit: Also, I just noticed the >800 amps, although I believe it's pretty close base on the math above.