New computer crashing while gaming - potential PSU or GPU issue?

Hello,

Three weeks ago I bought a brand new computer. It is a prebuilt Cyberpowerpc with the following specs:

Intel Core i7-9700K 3.6GHz (not overclocked)

NVIDIA RTX 2070 Super 8GB Graphics (latest Nvidia drivers)

16GB DDR4

1TB PCI-E NVMe SSD

Amazon link here

I primarily use my computer to run flight simulators, which are pretty resource-heavy. Everything was fine until yesterday when I fired up X-plane, and about 2 minutes after loading, my computer went completely powerless. The only way I could reboot was by toggling the power switch on the PSU to off for about 5 seconds then back to on. I tested X-plane again and got the same result.

My next test was to run Prepar3D (a similar flight simulator). It ran fine for about three and half hours, making me think the issue was something weirdly isolated to X-plane. However, today I did another test with Prepar3D and it crashed about 5 minutes in. I had been monitoring my CPU temps during all this, and noticed they never exceeded 65C, so I don't think it is a temperature issue.

I downloaded OCCT and did a PSU stress-test. As expected, the computer crashed. I took a short video of the test here, which shows it running and powering down: https://gfycat.com/revolvingsmoothalaskanhusky

The temperatures look fine to me, so I'm thinking this might be a PSU issue? Is that feasible for a pre-built computer like this? I don't know too much about PSUs but it seems odd it would only fail under higher-stress conditions. Is there any other hardware components I should be looking at?