"80 Plus" doesn't not guarantee the quality of the PSU though...Ezcool came to mind.
Also, I just looked up the spec of the Sumvision 450w PSU...it doesn't even come with native PCI-E 6pin connectors meaning it's not meant for a system with a graphic card that's higher than bus-powered. You are using molex to PCI-E adapters at the moment ain't you? Also, it has only 14A for the 12v rail (168W)...your graphic card alone at max load would consume that much power, and won't have any headroom left for powering the rest of the PC, CPU etc...and you are wondering why you keep getting crashes.
Seriously...save up and get yourself a decent PSU, rather than keep trying your luck on getting away with using a £13 generic 450W PSU for a quad-core system together with a graphic card that require two PCI-E 6pin power...