Is there any safe way to test this for a server PSU? As in "unlikely to blow the PSU", potentially requiring slight pre-checking by looking at the circuit?
I would be very surprised if you could find any non-ancient (and I really mean ancient, like, pre-PC, probably even pre-home computers) computer PSU that you couldn't feed with DC. What voltages will work will vary, but as long as you stay below the peak voltage corresponding to the effective voltage printed on the label, you probably won't damage anything.
If you really want to test it, you could measure the resistance at the mains input, if that gives you a non-infinite value that stays at that value (rather than increasing towards infinity), you are dealing with a mains transformer. But you really won't find that in a computer PSU.
~240V fully rectified to DC is 340V. Since AC varies it's safe to say virtually any PSU that's not exclusively Japan or North America will take 350V DC.
Well, you probably can somehow power it up without a server connected to it?
Active PFC tends to be simply a boost converter at the input stage that boosts the (rectified but still unfiltered) input voltage to (DC) 350 V or more, modulating the current to follow the mains voltage and should generally have no problem with DC input, especially so with wide-range inputs that have to be able to deal with different voltage levels anyway.
>modulating the current to follow the mains voltage and should generally have no problem with DC input
I'm particularily worried about confusing that following/regulating circuity. If the 50/60Hz it senses are caused by screen refresh feeding back somehow, it might end up behaving "weird".
But I guess I'll just try, and hope it won't break anything.
If it weights 5KG+ (12pounds), likely it is not a switching power supply as it has a bulky transformer (I can't imagine a server PSU not being a switching one). Other than that laptops, phone chargers, etc. would work off DC. Most of them use a small transformer and high frequency (above hearing range)to drop the voltage.
The transition is something like: 90-240V AC (50-60Hz) -> DC (1.414*AC) -> AC high frequency ->(transformer) AC low voltage -> DC 12V
Very cheap electronics that use capacitor+resistor voltage drop need AC.
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To answer the question directly, use a small fuse 1-3A and run the PSU idle. Like advised by sibling, measuring the resistance would be sufficient as well.
I would be very surprised if you could find any non-ancient (and I really mean ancient, like, pre-PC, probably even pre-home computers) computer PSU that you couldn't feed with DC. What voltages will work will vary, but as long as you stay below the peak voltage corresponding to the effective voltage printed on the label, you probably won't damage anything.
If you really want to test it, you could measure the resistance at the mains input, if that gives you a non-infinite value that stays at that value (rather than increasing towards infinity), you are dealing with a mains transformer. But you really won't find that in a computer PSU.