Gpu or Power supply Problem?

So i have a alienware 17 laptop now recently its powercord broke and i brought a new one but the new one is for a alienware M17 how ever it has the same Volts,Amps and Watts as my old one did. The problem is since i got it my laptop has not been able to run high gpu games insted they freeze or give me a black screen. Now i checked the gpu the temprature is normal but it is running only 35% of its ability and says its not getting enough power. Now it could be this cord as it does slip out the socket alot and the problems came after i got it but i dont know much about laptops. So is the powercord doing this or is my gpu dieing?