I use this psu:
https://www.amazon.de/gp/product/B01MRSAT39
It provides up to 20 A. It should be enough for 7-8 HC2 starting up together with the switch, the wifi mesh unit and the fan. I estimated 12V 2A, 24W peak power use per HC2. There are plenty of 5A or 10A similar power supplies. Currently 6 HC2 are running from the psu, together with the switch, mesh and fan. Works fine and since there is no fan in the psu it is completely silent.
I also bought some power cords that I cut off, crimped together in groups, and used between the psu and the HC2s. A lot of 12V cables...
https://www.amazon.de/gp/product/B078BKW6Y8
I have measured total 70-74 W power use from the wall when everything is running with low load. When booting and spinning up the drives, or under high load the power use is higher.