windows 10 – Why does my laptop PC continue to crash out of nowhere?

I have been working with a Fujitsu Celsius H730 workstation with Win10 Pro for just over a year now, and recently it has started to crash seemingly out of nowhere (it just shuts off without any warning). After a crash, it boots normally without any warnings that the PC crashed. But then, after a while (somewhere between 1-5 minutes after reboot) it crashes again. After several times, I discovered that unplugging the AC adaptor and running it on battery helps prevent a crash, but as soon as I plug it back in, it crashes instantly.

So I went to a repair shop (I do not have warranty on the laptop anymore, unfortunately) and tried to reproduce the problem, but of course it worked perfectly. The technician checked the AC adaptor and said that the voltage was fine.

After that, I got fed up and switched to an older laptop for a couple of weeks. Last week, I tried it again and it seemed like it was working just fine for just about a week, but now the same thing is happening all over again. I know that there are probably lots of possible causes for it, but maybe someone has a hint of what might be happening here.