Alienware 15 R2 battery not charging while gaming

I bought my Alienware 15 R2 laptop a year and a half ago, and i started to get this problem a couple of months after i bought it. When i try playing a game like Arkhum Knight i get every 3 to 8 seconds lower brightness screen because of the power modes setted like that. So charged in and off mode flickers every 3 to 8 seconds. I have updated all of my drivers including bios, i have no idea what to do. 

By the way, my adapters output is 240W which i think should be enough for a laptop.

My Specs: 
CPU: Intel Core I7-6700HQ

GPU: GTX 970M
Memory: 8Gb

Windows 10 (64bit)