PEGs are the the power cables by just about everyone, including Toms Hardware.
Even though the specification allows for a delivery capability of 75 W (six-pin connector) or 150 W (eight-pin connector), the total power-handling capacity of these connectors is at least 192 and 288 W, respectively, using standard terminals, and even more using the HCS or Plus HCS terminals.
These two auxiliary power connectors are sometimes called PCI Express Graphics (PEG)
All together, a graphics card could theoretically have a power consumption of up to 300 Watts. And, as you can see, regardless of which graphics card you use, there is more than one way for power to be distributed to it: 75W at 6.25A, just from the PCI-E slot, and up to another 200W (at around 17A) from each PCI-E Graphics (PEG) connector.
Case in point, PEG connectors.
6-pin and 8-pin PEGs have the same amount of 12v wires. True story, 3 apiece, although in the 6-pin, one might as well be disconnected because it isn't needed. The 6-pin connector is rated at 8A (itself a safe spec), but the pci-e spec is 6.5A (75W). So each 12v line pulls 2ish amps max in a 6-pin plug...compared to a molex plug that is specced at twice that, and rated for three times as much. The 8-pin uses all three 12v lines, and pulls up to 4A apiece (150w/12v/3=4.16_A), the EXACT same as the molex spec, but uses an enormous amount of grounds. If you can subtract, you would say 5. You would be right. If you think that is overkill, you would be right.
The Radeon RX 480 is based on a much smaller 14nm fabrication process, as such you will see many enhancements in efficiency and that shows in power consumption, the reference cards will use just one 6-pin power PEG (PCI Express Graphics) header to give the the card its power.
According to Nvidia, the lack of a PEG connector makes the Geforce GTX 750 (Ti) the ideal upgrade for "your neighbour's PC". Many of the OEM machines manufactured by companies such as HP, Acer and Dell do indeed have a PCI Express x16 expansion slot, but no power supply with a PEG connector.
etc, etc, etc.
But I have grown bored with the "But, but, but NVIDIA" crap. Let's get back to the issue at hand ... the RX 480 draws too damn much from the PCIe slot, which has 5 connectors rated at 1.1A each for a total of 5.5A, and at 12VDC, that is 66 watts.