I suspect that there is an internal power regulator failure
Yes, random shut off suggests it might be in the power supply. Since it is without warning, it probably is not something which Windows detects and does anything about.
I'm going on the observation that when my laptops have developed some serious problem, it would freeze, or go to BSOD. Or there would be a hang on startup sometimes, or refusing to respond to the On button other times.
Does anything different happen if you power from adapter only? batteries only? From both together?
Can you monitor voltage close to the incoming power supply? To see if voltage drops at the moment of shut-off?
Can you push or prod components to cause shut-off? This is a very risky thing to try, but it may help you track down the problem.
Can you insert a current measuring instrument in the power supply wires? This is risky, but you might observe a sudden current spike at the moment of shut-off. This could tip you off to a faulty component.
Have you examined logs of system events, application events, etc.?
Before the shut-off occurs, can you open Device Manager, and check the list of devices to make sure all are operating normally?