Seeing this old thread, and feeling the need to further correct misinformation so that others who might come across it don't become confused by the lack of accuracy, let's be clear that you are not "being safe than sorry" by simply getting a higher capacity crappy power supply. You'd be a lot more "safe than sorry" by looking into high quality models of the same (Or in some cases, even LESS capacity) than you would by getting a higher wattage, but still crappy quality unit. Further, as we try to explain to everybody who has difficulty grasping the concept, not all 750w (Or any wattage you'd care to name) units are made equally and the majority of poor quality units cannot even achieve or maintain their rated watts, so getting one with more watts on the label if it can't supply it, is simply a false sense of security.
Sorry for the necro, but if I came across this thread others have as well.