The one that is specified for Alienware systems will work. [URL]#techspecs_section  
i need to replace my power brick for the G15 5511 which is 240w. On the web site under accessories it lists only a 180w which I don't believe will drive the laptop. Accessory listings are misleading as I purchased the docking station assuming it would also charge the G15 5511 but it won't. How can I find and order the proper power adapter?   Thanks
Power Brick for the Dell G15 5511 - 240w not found