Power edge 830 and UPS "issues"

I have a Dell 8300 porridge server with a 450 watt power supply that is  about 6 moos old. Today I tried to put it on a UPS with no success.

 

The DELL was plugged into a Belgian 900 VA unit and , as per the Belgian tools, the Server was drawing 28% of the load rating of the UPS. I removed the USB cable and  then pulled the wall plug on the UPS  to test. Immediately the  Server shut off/ rebooted/shutoff/ etc until I pulled the plug on the server. This shutoff/reboot/ etc was in a 2 or 3 second interval- very rapid. The USB cable was not connected between the UPS and the computer so the UPS was not telling the server to shut down. In any case the shutdown was not a controlled shutdown, it was a "power off" shutdown.

 

Thinking the UPS may be faulty, I then tried the same setup on a Cyberpower Model 1285 ( a 1200 VA unit AFAIK). The Cyberpower indicated the Dell was drawing 175 watts- 15% of full load. When I pulled the plug on the CyberPower, the same thing happened: the Dell went into the same poweroff/restart/poweroff cycling as before. Once again, there was no USB cable between the UPS and the DELL so it was not being told to shutdown.

 

Both UPS are less than 6 months old. The diagnostics in the UPS do not show any discharge or low voltage on the batteries while the server is flip-flopping between off/on.

 

The shutdown I am trying to describe is like a power failure: it is not a controlled shut down and W2K3 server reports it as a power failure.

 

Any one have any Ideas how to a put a UPS on this beast?