None. It has the power cabling that goes into the HP Pavilion 790-0020's Berks motherboard and the one that's (currently) going into the "Slim"-type optical drive.
The system's storage is only its included NVMe M.2 drive. There are no "extra" or spare power cables/plugs coming out of it, which...
Well, the title basically says it all, heh.
I bought an HP Pavilion desktop and I'm very satisfied with it and now I want to add an extra SSD I have laying around but the custom PSU it uses has no spare SATA power plugs.
HOWEVER, the system comes with an optical drive which I have no need for...