One of the accessories bags contains these little doodads. What are they? Well, this power supply has a feature called "OCK," or "overclocking key." Basically, it's a way to disable the multi-rail overcurrent protection in the unit. You're not actually overclocking something. You can either use the little jumper on the left to permanently disable OCP, or plug in the expansion bay switch so that you can switch it on and off at will.
Folks, I'm telling you right now... this is a 1200 watt unit. Enough power to just about arc weld with. Try it with the multi-rail on first. Only use these doohickeys if the unit keeps shutting down on you no matter what cable combo you use.
See, this is why the "single 12V is better" thing is a myth. Sometimes, the bigger units of that ilk don't shut down when they should. They have too much current capacity. That's why my mining rigs are all running multi-rail when possible, even though they all have up to six video cards. If you plug things in right, and the power supply was designed correctly, you should never have an issue with multi-rail OCP shutting the unit down on you. But I've ranted enough about that before... I don't feel like getting into it again.