@naeshelle A straight restart of the computer is most often a power supply issue, so yes, that's a distinct possibility. But the PSU you have should be more than sufficient for your hardware. It's possible the unit is faulty or not running properly, so please look at it and make sure the fan is spinning when the computer is on. The fan also needs to be pointed towards a source of fresh air, not against a solid case wall.
Additionally, if your house or apartment is older, please plug the computer into a different outlet, preferably through a surge protector, but you can leave that for later if you don't have one. If you're already using a surge protector or power strip, test with a different one or with none at all. Dirty power from the wall can mimic a PSU issue.
If you're comfortable opening up the case, please also disconnect all the power cables, on both ends since the PSU is modular, blow out the connectors both ends) with compressed air, and reseat them. While you're working inside the case, have a look at the motherboard as well. You're looking for bulging capacitors—do a Google image search if you want examples—and anything that looks like a scorch mark.
I don't see any BSODs listed in your dxdiag, which supports the idea that this is a hardware issue and not a Windows-initiated shutdown. Still, please look for any associated crash dumps here:
C:\Windows\Minidump
If you see a file that corresponds with one of the restarts, please upload it to a free filesharing site (Google Drive, Dropbox, etc.) and link it here. I don't need older files though, just anything related to the current issue.
The problem is definitely not that you have too little RAM. At most, that would cause Sims 4 to crash without taking down the entire system, and 16 GB is enough memory anyway. Defective RAM is another issue entirely, but it's much less likely to cause a restart than a problem with the power supply or motherboard.
