Dell 3620 PSU upgrade

I am upgrading the PSU in an old Dell 3620 and I understand that the 8pin power connector on the motherboard is a proprietary dell standard and that I need an 8pin adapter - no problem, I've got one ordered. 

I just want to verify that the "P2" 4 pin connector is not also proprietary, I cannot find a pinout diagram anywhere. I assume it is standard but don't want to fry it based on an assumption. 

Bonus question; Is the P2 connector even required if the onboard sata power connector isn't used? Is that what the P2 plug is powering?

https://www.dell.com/support/manuals/en-nz/precision-t3620-workstation/prec_t3620_om_pub/system-board-components?guid=guid-d9eaa4a4-9cbc-445f-9845-75d8f7c620e8&lang=en-us 

https://www.dell.com/community/en/conversations/optiplex-desktops/optiplex-proprietary-8-pin-and-6-pin-pinout/647f8f68f4ccf8a8de077d92