Question Motherboard problem or PSU problem?

[Hypershell]

My computer built in 2020 (upgraded occasionally since then) has been "haunted" for the last month or so with random shutdowns. Used to restart on its own but more recently it requires cycling the PSU on and off (MB and case lights are on, all fans are off). Been checking for problems with RAM, GPU, drivers, and Windows to no avail (also had to clear CMOS once or twice due to crashing in the middle of startup).

Last night my wife couldn't even get it to turn on. Powered on for me fine, I used it a few hours, had no problems. This morning, won't turn on for me. Clear CMOS, nothing. Disconnect power button and try shorting pins. Doesn't work at first, does eventually with repeated tries. And that problem is now persisting.

PSU is an Antec NeoECO Gold 700W. It has received unstable power from the wall a couple months ago (bad UPS battery), but it has never cut out completely. Motherboard LED was still on after all crashes.

Motherboard is Asus X570-P, BIOS version 4002. It has given me two minor issues in the past: Chipset fan doesn't always start (Fan Control can always kick it on from Windows), and during a POST it will sometimes give false alarms about not finding a display but then POST anyway.

So, I highly suspect the motherboard is bad, but could it be the PSU? How would (or can) I check the PSU before buying replacement parts?

 

[JohnBonhamsGhost]

Antec NeoECO Gold

there are many different versions of the NeoECO Gold.
some are much lower quality than others, best of the line is even subpar for gaming or other high resource activities.

which specific version?
sometimes can tell by the color of the sticker/label attached.
should have more of a model description here also; Zen, F, II, etc.

 

[Hypershell]

there are many different versions of the NeoECO Gold.
some are much lower quality than others, best of the line is even subpar for gaming or other high resource activities.

which specific version?
sometimes can tell by the color of the sticker/label attached.
should have more of a model description here also; Zen, F, II, etc.

Sorry about that.
Zen. Model X7000AO15A-19. Yellow and black label.

 

[bill001g]

You are pretty limited in what you can test on a power supply.

You can look up the paper clip test that allows you to turn on a power supply outside a computer. You can then measure the voltages with a multimeter. This though only verifies very basic functionality. You can not easily test for example if the voltages drop as you increase the number of watts you are using.

My guess would be the motherboard since even if the motherboard does not boot you would think it would turn on the power supply. Unless you have a very fancy power supply the fans on the power supply always run when it is turned on.