[TriLUG] Hardware stability issues

[Wes Garrison via TriLUG]

Dear LUGgers,

My children and I have built nearly-identical desktop machines, and only
one of them is experiencing seemingly-random hard-locks (requiring 4-second
power button press to turn off).

Both machines are:
AMD Ryzen 5 5600G processors with built-in Radeon Graphics
MSI B550M-Pro socket AM4 micro-ATX motherboards
32GB Crucial Ballistix RAM
Debian 11

The only obvious difference is the power supply.  My daughter's computer
has an Antec 400W PSU, and my son's has a BFG 550W PSU.  My son's is the
one experiencing the hard-locks.

I'm currently running a memtest86 on the machine, but in my experience it's
almost never a RAM or processor problem.

Do any of you have a great way of isolating frustrating problems like this?

I *hate* throwing hardware at a problem trying to troubleshoot.

What would your first steps be?  Swap the RAM between the 2 machines?  Is
there any reliable way to test PSU voltage stability?

Any insight is greatly appreciated!

-Wes