I'd be VERY wary of using this PSU.
336W rated on the 12V max, unsure of actual 12V output capability without seeing the label, (quality 500Ws actually do provide near 500Ws, take the antec neo eco 520C for example, it puts out 40A/480W on the 12V supply). It is not 80+ Certified, comes with a 1 year warranty (most quality PSUs are 3 - 5 years), doesn't even look like it has active PFC. Basically this is very low quality, and not recommended for anything that you might care at all about.
You'd be far far far better off with a Corsair CX430 for near the same price. It provides just as much 12V power, more reliably and is of far superior build quality (despite not being that great).
Sorry didn't realize this post is days old, my condolences to those who bought.
And when it says 336w on the 12v rail, they mean it can do at least 336w on the 12v rail. This PSU isn't a 500w, but it does seem like a decent and cheap 400w.