Even if its a Diablotek and is capable of powering on the system, I personally wouldn't use it, it is a tier 5 power supply in this list:http://www.eggxpert.com/forums/thread/323050.aspx
Tier 5 should be avoided, though do realize this list was created by a person not some power supply company so it is opinion. Though they did a really good job with it.
Edit: Looked around and the HD 7770 uses around 12 amps for itself, either way you are golden with that VP-450. You got some room to OC if desired.