We placed a EATON Ellipse Max 1500 (900W) as the UPS for our HP Proliant ML350 G6. Upon first power failure (actually we only moved the UPS' input plug to a different socket), server immediatelly turned off, and the Health LED turned red and started blinking. UPS was in operation for about a week before that, with battery fully charged to 100%. Since our server's hot-plug supply is 460W, we are pretty sure we haven't overloaded it, the server was completely idle at that time (no web or win apps running except Windows Server core services).

Then we tried to do the same with a different, no-name older PC (Core 2 Duo, 2Gb RAM) with a generic power supply (not sure what the power is) and it continued working when we pulled the plug out. UPS load was less than 15% (measured in the provided Eaton utility).

We measured the UPS' output voltage using a smart oscilloscope and the THD of the UPS output waveform turned out to be 40%.

Did you have similar experiences? Could this be a faulty UPS? Or a faulty power supply? Or some HP sensors configured to trigger too strictly?

I wouldn't like replacing this UPS with the same brand, to get same results.

[Edit]

I also tried to do this while the server is turned off. While the UPS is working on battery, server will not start - as soon as I press the power button, Health LED starts blinking red.