The HP Proliant G6-generation (and newer) servers have a new type of high-efficiency power supply that is sensitive to the waveform output of UPS units. If you find your UPS is not carrying the new G6 server (it immediately shuts down upon power loss), check the specifications of the UPS unit(s). The output must be True Sinewave. If it is anything else (Stepped Approximation to Sinewave is the usual alternative), then the server will not run on it.
Advanced Logic Industries
Technical Assistance Center (TAC)