If you don’t want to be digging around in your case with a multimeter, but are pretty sure that your crashing is caused by a bad PSU, BigBruin has a review of the tool you want.  The FrozenCPU ATX 2.0 PSU tester is about the simplest way out there to check your PSU.
“When it comes to troubleshooting hardware inside your computer, any enthusiast can tell you that any particular problem can be caused by one or more components going/gone bad. Narrowing any problem down can be quite challenging if you do not have extra components lying around to swap in for the suspected bad component(s). Any help one can get in troubleshooting components is more than welcome in my eyes.”

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