Yup, that's half bridge alright. Out of curiosity, what are the switching transistors? If they were 13007s, then I wouldn't be surprised at all if it couldn't deliver more than 300W. I've found that to about the limit of 13007 transistors.
It allso lacks APFC, which is required for 80plus certification. There's no way that would comply.
I have recieved an email from 80plus requesting some internal pictures of the Aywun, which I have now sent. I'll keep you posted on what happens.