I handle a number of server power supplies, telecom 'rectifiers' and other like sundries, varying in power from tens of watts to 4kW and more. Any PS over 100W has the ubiquitous '100 to 240V a.c. input, unity power factor with sine current waveform'. This is all very well but for the fact that they draw, and need to draw, tens of amperes inrush current at start-up. Any hiccup in the PFC would blow the fuses, and more than likely, their switching mosfets and fast rectifiers.
I tend not to plug in any unknown PS directly, but with a current limiting tungsten filament lamp in series. This allows up to ten times the lamp's rated current through for the first half-cycle, decreasing rapidly. A 100W lamp on 230V mains suffices for PFC's up to 250W or so. For large (4kW) rectifiers, I have had to use 1000W halogen lamp! If the PFC has a shorted mosfet, the lamp simply lights up inviting you take a look inside. If the PFC is indeed good, the lamp lights up briefly and goes out; or more likely, the cycle repeats a good ten times until the PFC fills up the dc bus capacitors. Each time, a relay bypassing the inrush limiting resistor or thermistor, clicks.
A gradually increased a.c. input from a variac is useless here, as the PFC is held off till some 90V is reached, after which all hell breaks loose.
I would be interested in learning if there are any better ways of testing unknown rectifiers.