Will a PSU with Active PFC Work with Normal UPS
It depends (but most likely yes.)

Active PFC controllers will shape the input current to whatever input voltage waveform is sensed. The current will be as non-sinusoidal as the voltage, but will be in phase with it. The closer your UPS output is to a proper sine wave, the more likely your active PFC will work just fine.

That being said, there's a strong possibility that even with a square or trapezoidal waveform, the PFC may still 'work' with some degradation (noisy operation, reduced power output, etc.).

(I use an Antec-supplied ColdWatt active PFC front-end PC PSU with an older APC UPS - which provides a squarish sine wave - and things are fine. I also design PFC converters for a living.)

EDIT: No FUD here, I don't design UPSs but often have to make my PSU "work" with a square wave UPS for one reason or another.

The performance of the power supply when presented with a square-wave input will depend on many things.


The active PFC controller. There are some reduced-pin-count parts that don't actually have input waveshape sensing and some firmware-driven PFC microcontrollers that expect a sine wave, that could produce output without the PFC function (input current in phase with input voltage).
Input undervoltage sensing is often done by peak detecting the incoming sine wave and comparing it with a fixed reference. The relationship between peak and RMS obviously differs for a sine wave and a pseudo-sine or square wave, so you can see problems like the start-up RMS voltage being higher when the input is square vs sine.
The square edges of the input AC waveform can cause acoustic noise to be generated in the input EMI filter magnetic components and ceramic capacitors (Y-caps). Also, the fast edges will cause higher peak currents (vs. a sine wave) as the EMI components are charged and dischared per-cycle.