Your PSU numbers look good, if they are for real, but that is a kinda 'no-name' or generic PSU. Still, you should be fine there.
This sounds like your CPU (or some other component inside your case) is getting too hot, after a period of intense use. (game playing qualifies, perfectly)
The next time it 'crashes' on you, when you reboot go straight into your CMOS to your 'Hardware Monitor' page and check your CPU and System temperatures.
You could try pulling one side off of your case, and set up a small desk fan blowing cool air directly into the box.
See if that helps.
If it does, then you'll KNOW that it's a heat problem, and now it's just a question of 'Which component?'
This is the 'quick & cheap & dirty way' to find out if something is getting too hot.
But it WORKS like a charm!
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