The 8-pin connector for CPU (the EPS12V Connector, also called EATX12V) is rated for 7 Amps per wire pair (4 pairs at 7 amps = 28 amps), and is rated for 336 Watts maximum (12V * 28 Amps = 336 Watts). The 4–pin connector only has 2 wire pairs, and thus can only carry 14 Amps, for 168 Watts...