Everywhere it is said that you MUST have a powered risers if you are going to use more than 3 GPUs per mining rig. Now that I got my Asus R9 290's, I noticed that there is a separate PCIe power input in them.

So I'm just wondering; what exactly is the purpose for the powered riser, vs. one without a power? Are powered ones needed only with some older GPUS's without a dedicated power input? Do ALL R9 cards (270,280,290) a PCIe power input, so there wouldn't be a need for a powered version of the riser at all?