XPS 13 2015 random shutdowns

As per post title, my XPS 13 9343 shuts down randomly, even while not running foreground programs.

When I check the bios log, power section, it displays: 4 seconds power off, or ACPI management power off, or Power button. Like if I press the power button to shut the PC down.

When I try to run boot diagnostics, it will shutdown after 2-3 minutes.

When this happens (all the day), I check temperatures on bios and it shows normal temps (CPU around 60°, SSD around 30°, etc.)

Since my warranty is off, i opened the PC, disconnected main battery and cmos battery, pressed the power button for 10 seconds, attached everything, powered on and it lasted 3-4 hours without shutting down. After doing this, I ran diagnostics and it managed to complete all the tests without finding any problems (I also played a 3d-intensive game for testing, as prior to hard resetting it, opening a game would turn the PC off within the first minutes).

I reinstalled Windows countless times, downgraded to Windows 8.1 to see if 10 was the problem, but the problem is still there. Even in safe mode it will shutdown.

I am in serious difficulty now, as I need my XPS for live performances and I cannot rely on it anymore. It is causing me a lot of problems and I am extremely frustrated and will never consider of buying a dell product in the future. I put my trust in dell when buying this 1100+ EUR computer and it has failed me in a way that's impossible to solve without wasting *lots* of money and time on it.

Regards