I have a 600W UPS, as initial bed heating spikes to 1000W at 220V, this UPS becomes overloaded and shuts off. With a trick of manually incrementing the build plate temperature with a step of 2 degree at a time till target temperature before starting the print avoids the 1000W spike and is limited to ~300W and I am able to run the X1C + AMS combo with 600W UPS. I guess one feature can be added in printer to heat build plate slowly to reduce wattage requirement for UPS.
My understanding is the printers just switch mains power on and off for heating. In that case, you’ll still draw high wattage even though pulsing for shorter times. Apparently that doesn’t trip your UPS but it’s a kludge and I wouldn’t recommend it.
Since you are running a UPS, can you set the output voltage to 120? Running the printer on lower voltage is the only way to reduce wattage on the heaters.