How to power two 12 hdd backplanes with an ATX PSU?

I recently bought 2 12x 3.5" hdd supermicro backplanes that have 3 molex connections on the back that I was planning on powering with one of the two ATX PSUs I have laying around. (I do not want to use server PSUs because I am trying to build a quiet rig to replace the loud rackmount ones I have).

I assumed I could use a molex cable with 3x molex connectors on it to power the backplane but it turns out neither PSU has such a cable nor do they even have a molex cable with 2 molex connectors on it. Even if I were to get such a cable from the manufacturer would it be advisable to connect the backplane to one string of 3 molex connectors?

The PSUs I have do have cables with some sata connectors and one molex on the end. Could I possibly use a sata to molex adapter in order to populate all 3 backplane molex connectors with one cable? I assume this isn’t advisable because sata connectors are only rated for like 50w whereas molex connectors are rated for much more.

Whats the proper way to power such a backplane with an ATX PSU?

After doing some researching I learned that hdds require 5v and 12v power. Most power in a psu comes from the 12v rails so even though I assumed that a 750W PSU could handily cover the ~240W required by the hdds it may be limited by the output on the 5v rail. The 5v rail is rated for 20A, or 100W. Assuming hdds draw 1A on the 5V rail at startup this means about 24A at peak usage. This is definitely over the limit but if I configure my hba to sequentially boot the hdds would this be an issue? A failure in the HBA would be a risk in this scenario. Does anyone know of any ATX PSUs with 25A or 30A on the 5v rail? Assuming the 5v rail isn’t a limiting factor, what would the bottleneck be on the cabling? How many molex connectors can I power with one cable from the PSU?