Guru 3d says you should have at least a 450w.http://www.guru3d.com/article/his-radeon-hd-5670-iceq-review/5http://extreme.outervision.com/PSUEngine
.... says you have enough..
ATI says the minimum you want is 400w.http://educations.newegg.com/tool/psucalc/index.html
... says you have enough as well
You are right there for wattage, I think 400w is fine if you are using a good brand, but that brand is not good at all and I wouldn't trust it being pushed to the max, that’s for sure.
Even with the 4670, ATI recommends a 400W, so again you're probably pushing it, and with a bad brand, I wouldn't do it.