It's a 24 pin connector for the main and a 4 pin for the 12v. You will find that on slightly older PSUs they will have a 20+4 pin ATX connector or a 20 pin ATX connector - versus what most new PSU come with and that is a 24 pin ATX connector. All motherboards have a secondary connector that serves the 12v ATX connector and it could be 4 pin, 6 pin or 8 pin. In some cases you might have to get an adapter. That ATXP41 connector is an extra power connector, it serves to help stablize the power needs along the PCIe line. It isn't always used and is actually more of a safeguard that you COULD use.
Here's a link for an article about the various PSU power connectors that might help youhttp://www.dansdata.com/psus.htm