Had a good question so thought id share it. Save yourself loads by adding a power molex to your extenders as to not blow your motherboards with more than 4 cards in it...
Basically its 5 wires that go to YOUR YELLOW cable on the molex. 3 from 1 side (including the red one) and 2 from the other(leaving the red one connected. Pic shows it better. Each PCI-E sucks 75W so after 4, drawing over 300W from a mainboard (unless a high quality mobo) isnt a wise idea. I blew a crappy gigabyte (which i say avoid the new ones, ive had 3 failures of AMD gigabyte boards).
By doing this you draw it from your PSU instead and skip the motherboard