New
#11
looks like only three on the original psu
HP ProDesk 400 G2 MT original Desktop-PC power supply 300 Watt - sparepartworld.com
I think it is standard ATX. If so any reasonable standard atx power supply will fit and have mutiple sata connectors.
That is probably easiest.
I think it was later than the prodesk 400 G2 that the proprietary disease took over.