Must be a misunderstanding. I checked several references. The brand new OCZ Z series power supplies do not come with a P8 or P9 power cable. Instead the OCZ Z series power supplies like other modern psu's come with a 20+4 pin motherboard power cable and a 4+4 pin motherboard power cable.
The P8 and P9 power cables and connectors were common more than ten years ago. Both the P8 and P9 had a single row of 6 pins. They were the primary motherboard power connections. They had to be plugged into the motherboard so that the black ground wires of each were next to each other. When the atx standards for motherboards were revised the P8 and P9 connectors were replaced by the 20 pin connector. Another atx revision led to the 24 pin connector.
Back then some power supplies came with a third P connector power cable. It was used on a very small handful of motherboards just prior to the introduction of the 20 pin motherboard connectors. Most of the time the the third cable was not connected to anything.