Yes it needs a load connected.
Here when we want to use an ATX PSU and no motherboard (say for powering a custom device) we use a special load connected to a HDD molex and jumper the ATX connector green wire (PIN 16 POWER ON) to a black wire (PIN 17 GND) to turn it on.
In the old days we used to use HDD's as the load but newer PSU's don't turn on with only a single HDD for load
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