There's a point you're all completely missing.  CPU connectors for the motherboard are 4 pin or 8 pin.  PCI-E power connectors are for graphics card and are either 6 or 8 pin.  The 8 pin CPU and 8 pin GPU connectors have completely different wire arrangements and different shaped plastic housing.  They are not compatible with each other.

The other point is that most high end power supplies are single rail.  That means stealing power from the 12V CPU power connector with some wacky chinese adapter to put it into a PCI-E hookup is pointless.  All the power is coming from one 12V rail anyway.

I would simply buy the right power supply instead.