Buildapc

Doesn't appear to be psu, that model is pretty reliable and I've never had issues with it. And especially with your specs, that should be well within the power profile of the psu.

There's a bunch of other strange things that can cause it. I would first check if everything is seated properly, especially if you use riser cables or extension cables. I've had a build that would have the display go black randomly, and the fans would start running at max speed, and the only way to return it to normal would be a full reboot. Turns out the riser cable was a bit loose and the problem goes away if you push the gpu firmly into the riser cable's pcie port.

If that doesn't work, I would also try reseating the RAM or CPU. I had another build that was prone to crashes at random, no idea why. Did all the regular troubleshooting things. I suspected it was a CPU issue, so I pulled out the CPU and plugged in my old CPU to test. When I put my new CPU back in, there were no issues anymore. I have no idea what I did differently, so it must have been that the CPU wasn't seated correctly, or something like that.

Anyways, connections would be what I would check first. Pull out the pieces and then reseat them one by one and hope the problem goes away. If problem still persists, I would suspect it's probably the riser cable. This might be a bit difficult with an SFF case, but try to mount the GPU directly onto the mobo, and see if the problem goes away. As I mentioned above, it might just be that the riser cable is a bit loose (so you might still be able to use it as long as you seat the GPU firmly), but it's easier to troubleshoot if we can confirm that the riser cable is the problem

Crashes under intensive loads can be almost anything: Thermal, Memory, f-ed up Harddisk/SSD, Mainboard, etc.

Try to eliminate each single cause: Heat the PC with a hair dryer without giving it a high load, run memtest, etc.

Try limiting the speeds of your CPU then the GPU and see if the crashing still happens. If you drop the CPU speed and it goes away then something is with your CPU (or memory). If dropping just the GPU stops it then it’s probably the GPU. If you have to drop both and then it’s stable, or dropping either CPU or GPU then it could be the power supply.

all my PCs have voltage sensors i can monitor/log. maybe that could help you. like on linux i used lm_sensors to check their values.

RAM instability can cause exactly what you're describing, especially at load. Run some tests to see if that's the culprit.

How old is your PSU? 600W should be plenty, since your CPU has a power limit of 88W, and your GPU averages 185W (worst spike I read about was 202W). Those two parts are pulling ≈300W at worst, and they're the bulk of your energy consumption.

An old PSU, though, will have failing capacitors and resistors, and it may not function correctly. It's usually recommended to replace them eventually, though I don't know at what frequency.

ETA: is your PSU getting enough airflow? Could it be overheating?

I've heard this in passing and haven't really been able to verify myself, but I gather that SFF PSUs are less resilient to transient power spikes (I.e. from GPUs), which can manifest as system instability under load.

There are several PSU tier lists floating around online (which I have also been meaning to consult for my own systems).

Sounds plausible to me. Usually you want to leave a couple of hundred watts of headroom on a PSU.

To my understanding you want some headroom for your PSU for spikes of power draw or moments like when large appliances start up. Ive certainly had psu's as the cause of failures like that so it seems like it could be the case. Maybe you could get a 750w with return policy and try it out. Worse case you can just return it within that period!