If an OEM part failed under warranty, provided it is entirely unrelated to your upgrade, you'd still be covered but you'd have to put everything back to stock OEM configuration before they service it. 
Hello, I got the Aurora R10 with the stated "Alienware 550 Watt Multi-GPU Approved Power Supply with High Performance CPU Liquid Cooling". I have a couple of pretty straight forward questions: - how could be that a 550W power source can be used as multi-gpu? - if do decide to upgrade on my own, to probably a 750W power source, will I void my warranty? Cheers
Aurora R10, 550W multi-gpu?