nukemaster :
I would almost guess a defect then. It is a real shame they did not help you out.
He said he got multiple same-model replacements and got the same result with all of them, so the same defect across multiple units seems unlikely.
~200W PSU output / 80% efficiency = 250W add an LCD and possibly other accessories, the total may climb above 300W. Depending on how the S12-II behaves when it receives a stepped approximation input, it could very well trip the UPS' battery or output over-current protection early.
My PC is low-specs compared to the vocal THG average but if I let FurMark + CPU Burn run for a few minutes, HWInfo will occasionally catch the UPS reporting my modest system peaking at 300W from an average of 250W. (That includes a USB hub, a handful of USB-powered devices and my main 24" display.)
Some GTX960 would be capable of tripping a 330W UPS all on their own:
http://www.tomshardware.com/reviews/nvidia-geforce-gtx-960,4038-8.html
Look at the total graphs (last image), they show the Strix peaking at 350W, that's 420W at 80% PSU efficiency even before adding the rest of the system. None of the others break 250W. Still, add 70W for the rest of the system, a 30W LCD, PSU losses and you are over 400W.