Computer reboots while playing games

[Spacebit]

I have a rather unusual problem.
Until yesterday I had Windows 10 build 1607, last updated somewhere back in February. It ran fine, and I played all my games comfortably. A week ago Diablo 3 came with an update, and right after that I wouldn't be able to play it more than 5 minutes - because the computer would suddenly reboot without any warning, and come to BIOS screen where it'd say it saved me from a power surge or something. I tried a couple of times more and the same thing repeated. Then someone suggested to change game client to 32bit, and I was able to play for 1.5 hours until it rebooted again, but this time with a BSOD just before rebooting. Then I tried Overwatch, and again rebooted within 5 minutes.
The Event Viewer in Windows 10 said these were something called Power-Kernel Error 41, I don't remember right. I thought for sure my PSU is failing on me, so I contacted Seasonic. They said it can be GPU related too, or overclocking, or CPU overheating. They told me to run a Catzilla benchmark to test the PSU.
Now, I monitored GPU and CPU temperatures with the ASUS AI Suite 3, and the maximum was 54 and 38 degrees respectively. I don't know how to overclock and have never done it. I ran Catzilla and at about 80% of the first test the system rebooted again.
I was also asked by everyone to update both Nvidia and Windows OS to the latest. Since I knew there's the Creators update available, and Nvidia came out with new drivers just today, I started the updating process.
Here's where it gets tricky. I downloaded the Windows 10 build 1703 ISO file and Nvidia version 384.94, clean installed Windows and installed all the drivers (audio, LAN, WiFi, GPU, etc.). Then I installed Catzilla and ran a test. It passed! The Catzilla benchmark test worked without any sudden reboot. Thinking that my problems have finally been solved, I updated Windows 10 to the latest (some 500mb). I ran Catzilla again. And this time it failed, i.e. I got the reboot. I tried one more time and again reboots.
I repeated this process again - clean install Windows 10 again, Catzilla passed, update Windows, running Catzilla reboots the system.
I clean installed Windows 10 again. This time I didn't bother with Catzilla. I installed all necessary drivers, prevented Windows from auto updating, turned off all Game mode and whatnot, and installed Diablo 3. I played for about 1 hour without any reboot. I played Overwatch without any reboot.

Now I don't know whether the PSU is faulty or not. And funny thing is Seasonic has accepted my request for RMA, I just have to ship them. But the PSU fan has a faint noise and increases when playing games, and few months back it made a coil-whine but only once.

Build:
Intel Xeon E3 1245 V3
Nvidia GTX 960 4GB
G.Skill 16GB DDR3
ASUS H97M-E
Seasonic S12G 550W 80+ Gold
Samsung 128 GB SSD for OS, 2x 2TB HDD for games
1100VA APC UPS

 

[LukeFatwalker]

The issue isn't likely that the PSU is faulty, it's more than likely that the power demands exceed the supply. So when you mention it's faulty, and they say it's not; they're not wrong, but they're not right either.

You can try sending it in for repair, but be prepared that if you get it back and it's 'fine' that you might have to replace it with one with a higher wattage.

Just be sure before you make any hardware changes to back up your PC, either Rollback Rx or Macrium Reflect are free tools that are also great backup tools.