Gigabyte doesn't have a 550 Watt model in the PoweRock Series.
If your looking at the GE-P450P-C2 model that one is from Gigabyte's Superb Series and is made by AcBel Polytech not CWT (i.e. Channel Well Technology). It is a 450 Watt continuous power supply unit that has a peak of 550 Watts.
The Corsair VS550 is better than the Gigabyte model because it can actually produce a continuous 550 Watts and has a much higher +12V rail capacity and it has two (6+2)-pin PCI Express supplementary power connectors.