I just installed a ASUS EAH4770 PCI Express video board into a machine a few years old. There is an "auxillary power cord" to connect from the board to power. The cord plugs into the board, then splits into two separate standard sized power connectors. Unfortunately, there was only one such available connector.
I seem to dimly recall something about this not being a problem, so I went with it by plugging in the the one, and leaving the other not plugged in. Then I fired the machine up and it works.
But I am wondering if something is seriously wrong with this configuration that is begging for trouble.