Frequent reboots since upgrading hardware (new MOBO, CPU, RAM, SSD)

I'm not too concerned with testing the old one. If this PC keeps running for another day with no reboots, I'll know the old one was bad. Right now I'm at 22 hours with no reboots, which is a positive sign.I would have had at least a couple reboots by now. I'll update again tomorrow.

EOF said:

Hmmmm...
I wouldn't mess to much with these psu testers. They are not reliable, especially if you use them on a psu without load...
Take care with the results of the testers.
I'm working as sys.admin in several companies and we have many of these testers and we had lot of false alarm ot even not detected bad psu by the testers.

Use a real multimeter not some cheapo plug in tester

You will run into the same problem like with cheap or not cheap tester.
It means almost nothing if you multimeter or tester show you a "in spec." voltage.
That info is far away from the info to say "yes this psu is ok or not.".

The psu voltage must be checked under load, under a specified load which depend of the power rating of the rail you test on the psu and the max output power rating of the psu.

or another situation:
your psu have a specified start up time, which can't be measured with a multimeter, this is mostly specified around 250ms rise up time. If this were out of spec, lets say it start in 50ms or 500ms your psu will could cause unpredictable problems.
But if you use a multimete, it will show a correct voltage and you would probably specify this psu as a good device.
A psu tester, even the cheapest one have a "rise up time" checking feature.

Conclusio:
To be really sure about the health of the psu it is the best way to change it to a new one.
This is a scenario for average users who
So, forget testing the psu with multimeter or tester.
Take a new psu and check the behavior or call a pro to solve the problem.

Since replacing that PSU (with the same exact model) two days ago, my PC has not rebooted once. I'm confident this is the fix. The bad PSU (Corsair TX750W) was bought back in 2011, so I'd say I got my money's worth :)

Thanks for all the tips and suggestions!

Andy

pepanee said:

Glad you got it working. But please, for future reference, or for others that may experience the same thing.
When I said you should check out Event Viewer, what I meant was that there should most likely be an entry in there if the computer was given the command to properly restart.
So, for clarity on the matter, when you say the computer is rebooting, which, of the two, do exactly mean?
1) All of a sudden, all your open applications begin closing, and your computer initiates the rebooting procedure. Then your computer will have the word "Restarting" in the center of the screen, with the little dots spinning in a clock-wise direction.
OR
2) You're using your computer. Then all of a sudden, your computer monitor turns black. A few seconds later, you notice that your computer is starting up, as if you just turned on your computer.

pepannee, I meant the latter. The screen went blank, PC went silent, then about 2 seconds later, it restarted.

I went back to the Event Viewer for a time/date I know it crashed (I was texting a friend about this problem, so I had an exact date and time to look at). I saw several Informational events (that weren't helpful at all) and the following two critical events. That's it for the time it rebooted:

The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly.

The previous system shutdown at 10:44:08 AM on ‎6/‎28/‎2022 was unexpected.

I used the procedure from the link below, using event IDs 41,1074,1076,6005,6006,6008,6009,6013:

Windows: Shutdown/Reboot Event IDs - Get Logs - ShellHacks

And it's still running strong as of this morning. Still no reboots. I swapped out the PSU on 6/28 at 11:50am ET, so nearly three days of solid uptime. Guess it's time to chuck that old PSU.

This is WAYYYY over due, but replacing the power supply DID fix my problem.