CPU stays under 0.80 GHz on startup for a few minutes then returns to normal speed.

So, I have a Dell Latitude 7490 and as the titles says its stays under the 0.80 ghz on startup whether it is plugged in or not. I did a little research, and it says that its due to low voltage detection, but it didn't happen until recently and I have tried every outlet at my home and university, still this happens. I have turned on High performance and CPU output thing is also set to 100% and I have only enabled the absolutely necessary services from the task manager. Also, the bios time is high, it was normally 6.6 seconds and now its 10.5. I would be glad if someone knows what's happening.

I have a 60W battery

8gb ram

core i5-8250U