On Tuesday 29 May 2007, Dan Halbert wrote: ...
Watts = Volt-Amps IF the power factor is =1. Power factor is based on the reactance of the load. A purely resistive load has a PF=1. Google << watts vs volt-amps >> for more info, e.g. http://www.vabiomed.org/documents/tech0003.htm.
The power supplies I have measured in servers have a power factor close to 1. But I have measured consumer machines with a power factor considerably different than 1.
Worth knowing here is that even if you have something with pf=1 you wont get those 1500 watts out of a 1500VA UPS. UPSes are often, what they call, power factor 0.9 or 0.8. This means that you'll never get more than 1200W or 1350W out of a 1500VA UPS regardless of the pf of your load.
That said, modern powersupplies I've tested lately have all been better than 0.9 and most even >0.97.
/Peter