OP, read this article:
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=246The PSU reviewed there is build on the same platform as yours. They are both manufactured by Andyson according to the same spec. The only difference are stickers, just like with reference GPUs.
Although it might come as a shocker, contrary to what the label might imply, your PSU is NOT capable of delivering 1200W in continuous mode.
Moreover, your PSU has all its 12V power divided into four rails, each of them limited to 40A (480W).
You need to take very good care when loading up these rails.
If you connect your PSU in such a way that one rail becomes overloaded, as the PSU heats up and as a loses some efficiency (so-called de-rating), it might shut off on you.
This is a half-decent PSU but the rail distribution makes it quite hard to connect it the right way.
You'll need to read the manual and figure out which connectors to use to distribute the load evenly across the rails.