You could take a look at this thread;
https://forum.45homelab.com/t/what-does-this-mean-regarding-ssd-s-from-the-printables-website/620
I can’t remember if any members who have maxed out the backplane and SSD caddy have posted which PSU they are actually using.
I think the issue is more around disk spinup than sustained load where you might get close to the 20A. I think the backplane is supposed to support staggered spinup, but I think that depends if you are using SAS drives instead of SATA or something IIRC.