I need a new PSU... Advice
Does your current PSU really do anything harmful as of now? Or you just suspect it will die soon or not be able to keep up? Can you stretch the life of your current one until you actually get the 2nd gpu?
Whatever you do, don't take a "risk" on a questionable PSU if that is the situation you are already trying to get out of! Some people go the other way, too, and buy an 1200w and never end up even going with more than 1 gpu. In other words, maybe wait 'til you actually order that 2nd card.
I went through 2 before I landed on my Thermaltake Toughpower 850 modular, which has worked like a dream for me thus far. In other words, I wasted money on 2 "cheapies" to get me by when I should have had patience and just went big and proper in the first place.