It's different for every model or a set of models, for example, the APW9's output is 14.5V-21V DC which is the same voltage for the APW9+, but each is suitable for different models, you can't mix PSUs, the miner won't start.

Also, it's isn't just a matter of matching the voltage, most new miners connect to the hash boards using direct busbars at a very specific orientation, so even if you managed to trick the firmware to accept a different PSU it will be hard to deal with the connectors, so long story short, it will be extremely difficult to use any PSU except the one that the manufacturer itself makes.

This is why one should always stick to buying the same model, doing so, you end up with spare parts to revive different miners, if you have 10 gears, one loses a PSU, another loses hash boards and the 3rd one loses a control board, you can mix the parts and end up with only 1 dead miner as opposed to 3, but if you buy 1-2 of every model, you will be in trouble.