Hi, I have an APC Back-UPS CS650 which outputs a stepped sine wave, and works perfectly with my passive PFC power supply. I'd like to know if it will work with newer PSU's which have active PFC.
There are a lot of discussions on the internet which suggest that active PFC PSU's work only with true sine wave UPS'es or only some will work with stepped sine wave PSU's.
According to APC knowledge base ( http://nam-en.apc.com/app/answers/detail/a_id/8883/kw/d... ) there can be a gap in output voltage that lasts up to 8ms when the external power fails, and this causes the PSU to drain its maximum power which overloads the UPS. So does that mean if a PSU can handle more than 8ms gap in the input, then it will be fine with the UPS?
For example according to the specification the FSP400-60APN has an OUTPUT VOLTAGE HOLD-UP TIME of 16.0 mS minimum (at 230V / 50 Hz, 80%LOAD).
I use a Corsair Professional Series HX750W PSU that has active PFC with my APC Back-UPS XS 1300 which uses stepped approximation to a sine-wave and it works absolutely fine.
Most power supply test reviews don't test for UPS compatibility. X-bit Labs is the only one whose reviews that I've read actually run the power supply on a UPS that uses stepped approximation to a sine-wave to determine UPS compatibility. Some power supplies don't work with this type of UPS.