Alienware 17r2 CPU Throttle Fix By Unplugging Power Adapter?

Firstly here are my specs:

Alienware 17r2 i7-4720hq

GTX 980m

8GB Ram

Windows 10

I've noticed games severely throttling my CPU to 800 mhz every know and then especially on Overwatch where after playing for 15 minutes the fps drops from 60 to 24 (frame rate cap on). I've the 180W adapter requested for the 240W but was declined by Dell.

However, just yesterday I realize that unplugging the power supply from the laptop and replugging it temporarily solves the problem. I could play for 3 hours without such a drop.

However, the problem comes again after a while and the only to fix this is to unplug and replug. 

Does anyone have a similar experience? Or is there something else that is causing this problem? Should I reinstall the bios?