You have a screw driver? If doing anything electrical, then meter is
useful. The tool is sold even in Home Depot, Lowes, Radio Shack,
Sears, and K-mart. $20 standard price; seen on sale for $10. Question
is not what you have. Question is what is needed. Once that power
supply is replaced, calibrate the motherboard monitor AND confirm
problem is really fixed. Do you assume replacing what was a good power
supply with a new power supply automatically fixes the problem? More
reasons why a meter and screw driver are both needed.

Martin wrote:
> ...
> Been in touch with the PC's owner again today and the problem is
> getting worse.
> PC now unusable due to it's rebooting.
>
> Haven't got a multimeter to test the PC's current PSU but we intend
> to replace it anyway.