Question Testing a PSU ?

Any easy ways to troubleshoot if he needs a new PSU?
Not really, unless you have expensive testing equipment.

The paper clip method is flawed, due to the fact that the test doesn't tell you how much power the PSU can effectively output at any given time.

One way to route out the issue is to source(borrow, not buy) a reliably built higher wattage PSU to power your troubled system with. What is the make, model and age of the PSU your friend is dealing with?

Best you include the specs to his build like so:
CPU:
CPU cooler:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
OS:
Monitor:
include the age of the PSU apart from it's make and model. BIOS version for your motherboard at this moment of time.
 
He just wants help taking out the PSU and installing a new one, and I thought maybe we could diagnose if that was the problem first.
Trying a new PSU is probably the most sensible option, provided you get a good quality adequately rated unit.

If you want to test a PSU thoroughly, as @Lutfij says, you need expensive equipment.
https://www.tomshardware.com/reviews/how-we-test-psu,4042-2.html



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At the very least I'd apply the highest load possible (CPU + GPU stress test) and monitor the supply rail voltages on a digital meter and the ripple voltage levels on an oscilloscope. Anything less and you're just guessing that everything seems OK (or not).

When the magic smoke appears, it's probably too late.
 
These guys are not wrong and all that advice should be taken seriously.

As far as "semi-helpful" there are some inexpensive PSU testers anywhere from around $10 and up to a couple of hundred dollars which are of widely variable usefulness and quality. Most of them do not test under load. I have seen various content creators use things like old drives or car headlamps to simulate load which may or may not really be useful. One thing for sure though, if a $10 PSU tester calls a questionable unit bad...