I wish I was joking about that but i'm not. 1500VA units are pretty much as bit as you can go on a 15A circuit, and the one I have is 1500VA but can only feed about 1.1kW as an "at the wall measurement". Pull more than 1.1kW from the UPS and it enters an overload state with alarms going off etc. I could trigger that under normal "gaming" loads.
Want to pull more than that and you really need to step up into the 20A class of UPS units.
The 6990 was power hungry, flick the bios switch to the second profile and it drew even more. Combine two of them and an overclocked 1100T, pumps, fans etc very very easy to break 1.1kW from the wall and that doesn't even account for monitor(s) which was 3x1080p panels at the time.