The Corsair VX450 with a +12 volt rail rated at 30 amps is an excellent choice for a system with a single ATI radeon HD 5770 video card.
Corsair power supplies have a reputation for high quality. They consistently earn high marks in technical reviews. They are stable, reliable, and come with either a 5 year or 7 year warranty depending on the model.
The general rule of thumb is a high quality 500 to 550 watt power supply with sufficient current (amps) on the 12 volt rail(s) can easily power a system with any single video card made. A high quality 700 to 750 watt power supply with sufficient current (amps) on the 12 volt rail(s) can power a system with two video cards operating in dual mode. There are a few exceptions like the new ATI Radeon HD 5770 video cards which use less power due to its energy efficiency.
Here are the ATI recommended power supply requirements for the new ATI Radeon HD 5770 and 5750 video cards:
450 Watt or greater power supply with one 75W 6-pin PCI Express® power connector recommended
600 Watt and two 75 watt 6-pin connectors for ATI CrossFireX™ technology in dual mode
That's for the entire computer system.
5770 Technical review: http://www.anandtech.com/video/showdoc.aspx?i=3658