video cards don't take all power from the 8 pin connector. They can also take up to around 65w from the SLOT. (officially it's 10w on 3.3v and 65w on 12v but recently I think they loosened the standards to allow up to 75w on 12v) i can run a 150w gts 250 just fine with molex - sata - 6+2 pin adapter, you can say its gonna catch on fire all you want but unless the cables get really hot and actually pose a risk of catching fire you arent gonne convince me, atm even if i stress it the cables seem to only get w arm, from what i can tell its around low 30c in temp

pin 8pin GPU Power Cable. Different shape and Empty pin

And third you can use daisy chained cables if they are proper 16AWG daisy chained cables, if you have something like an old Seasonic unit that shipped with 18AWG daisy chained 8 pins then don't use it.IF your power supply has only one 8 pin connector, the first thing you should do is to look at the label of the power supply and see how much current the psu can actually supply on 12v (doesn't matter how many adapters you have, if the power supply can only produce 250-300w on 12v) and second ask yourself if you trust the power supply to not lie about its capabilities on the label. If it's from a brand with decent reputation, chances are it's not lying. If it's some cheap model or some chinese psu that came with the case, most likely the psu is inflating the numbers. You shouldn't be able to switch between them - the square and rounded off connectors are arranged such that you can't. Note the top left connector on the EPS 12V is squared off, while that on the PCIe is rounded off in the image before.Essentially differences like that are to prevent you from plugging in a PCIe connector into a EPS12V. There may be other differences, but I don't have these connectors on hand/ You can't connect male EPS-12V to female PCI-E 8-pin because 1 male pin of EPS is square and its rounded on PCI-E.

8-Pin PCIe to Molex (2x) Power Cable Cable Matters (2-Pack) 8-Pin PCIe to Molex (2x) Power Cable

PCI-e organization imposed the limits of 75 watts for the 6 pin connector, and 150 watts for the 8 pin connector. Some PSU maker could use a different pinout on the PSU, so even if the pinout is standard from the GPU side, it is not from the PSU side.

I have a Antec 850 w - High Current Gamer ATX12V/EPS12V. I had a friend that came by with his Corsair cable and it indeed not fit. It seems that all the bottom pins have a bevel on the bottom and won't accept the square ones. This power supply have 2x 12v connectors.