EPS power connection on the motherboard is for CPU power, PCIe is the 8-pin is for Graphics Card, and some PCI-e devices, power. Although the cables themselves look nearly identical, EPS-12V and PCIe are not the same connections, and will not fit if you try to put one into the wrong one.

EPS-12V 8-pin connection utilizes additional 12V connection, which will allow a single 8-pin to provide 300W. For newer graphics card, such as the A6000, this will be enough to suppliment their maximumTGP(total graphicspower) of 300W. 

You can see that the PCIe 8-pin has one square shaped pin for pins 5-8, whereas EPS-12V has two square shaped pins in the same row. This will prevent inserting the cable into the incorrect slot, most times.

Credit to https://superuser.com/ for this image

EPS-12V Y-Adapter

Some graphics card that reqire EPS-12V may come with a Y-adapter that allows two PCIe 8-pin cables to output to a single EPS-12V 8-pin connection that plugs into the graphics card.

Credit to https://www.igorslab.de/ for this image