Max Wattage: 450
Peak Wattage: 500
...so is it safe to buy with the expectation of it working properly?
First of all, think of "Peak Wattage" as burst/spike wattage: the absolute maximum wattage a power supply can put out in brief spurts. Power supplies cannot maintain peak wattage output for sustained periods without damaging your components.
Maximum Wattage is the amount that the power supply can output stably, but even then it's usually recommended to overshoot the mark a bit. I personally wouldn't run a 5870 on less than 650, and I picked up a 750 Watt Corsair for my system just to be on the safe side.
It's also important to note the manufacturer of your power supply. When reputible manufacturers like Corsair and a few others advertise 750 Watts, you can be confident that that's what you're actually getting. With other manufacturers that isn't always the case.
I hate to tell you this, but running a 5870 on your current power supply is simply a recipe for disaster.
I would recommend spending some time browsing through the power supplies on newegg
and cross-referencing any deals you might find with the Certified Power Supply
list from ATI. Here
is the info on the Corsair I bought for my system if you're interested.
I'd hate to see you drop $350.00 on a great graphics card and end up having a lousy experience (or worse, damaging your system) because you didn't want to spend $80.00 on a solid power supply. Edited, Aug 15th 2010 10:25pm by akirussan