^^
an ACTIVE PFC PSU needs (and its is a must) a PURE SINE WAVE UPS..
APC's SMART UPS range of UPSes are pure sine wave UPS and ideal for ACTIVE PFC PSUes..
but... PURE SINE WAVE UPSes are way too costly than normal (Stepped/modified) sine wave UPSes and it is NOT recommended to use a stepped/modified sine wave ups for a ACTIVE PFC PSU as in future it will cause:
mobo unstability, "hiss..ss..ing" noises from the PSU (as if the psu is not able to draw full power), system unstability issues..
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Cheers n e-peace....