if you want a modular psu, the seasonic m12II 620w, OCZ ZT 650w or the Rosewill Hive 650w should fit your need. if you rather use a non modular, that corsair tx 650w, seasonic s12II 620w should cover it.
if you plan to sli, get the 750 watt psu.
for other psu recommendations at various price points, i labled in my sig.
Is this related to the psu's hold up time? I can't find published hold up times for the PSU's.
Hold up time isn't a commonly published spec. Most test reviews don't even test it.
Actually the problem is related to the design of the PSU's Active PFC circuit.
Some Active PFC circuit designs can't deal with a non-sinusoidal waveform when the UPS is operating in battery mode. This causes the UPS to fail the switchover to battery operation or it'll cause the UPS to report an overload condition with odd noises (e.g. groaning noises) resulting in the UPS shutting itself down.
I bought the Corsair TX650 and it seems to be DOA.
From Corsair's FAQs:
My Machine doesn’t start up when I hit the power button, is the PSU faulty?
Disconnect everything from your PSU except for one single fan that should be connected directly to one of the Molex connectors. Then, get a small piece of wire, paper clip, or suitable object and short the green pin and a black pin on the 24-pin connector on the power supply. The voltage present is a very low signaling voltage so no worries of being shocked. Your PSUs fan should spin along with the fan you have connected to it. If this is the case, your PSU may not be receiving the power on signal from your motherboard and you should consider other causes of the problem you’re having.
If that doesn't work then contact your vendor to exchange it for another new one.
You can also try powering it with a different power supply unit if you have access to one for testing purposes.
ko888, I have another thread on this and would be glad if you could contribute. Long story short, I am using this right now on a Dell mother board. The old Dell psu works with the mobo but the new Corsair psu does not.