Old PSU jiggered?

I'm trying to put together a system for my gran from some old bits, but it's a bit unstable and turns off rather abruptly now and again. The ram and cpu I'm pretty much certain are good, so I think it's either the PSU or mobo that's the problem. The readings in bios for the voltages seem rather low:
Vcore: 1.82
3.3V: 3.28
5V: 4.86
12V: 11.67
It's a Asus one that came with the case, it's only running an socket A Athlon 1800+, 512MB ram, 1hdd and onboard everything else. Do you think the low voltages are the problem or could it be a faulty mobo?

Yeah looks like a dying PSU to me, do a temporary swap and see if there's a change.

It could be the PSU overheating - is the fan working OK?

The fan is running but the air coming out seems to be rather toasty so probably is the PSU.

Don't think there's another spare PSU here so can anyone remember when ATX came about? The reason is my gran currently has a 450MHz K6 I believe, so maybe the PSU from that would do? Upgrading her to XP.......