look into, i think Delta's, laptop/desktop external PSUs, they hit the 87-90% but they are a higher voltage DC.
There is also nothing wrong with using a PCIe power adaptor off a desktop internal PSU
Perhaps domestic drivers for LEDs would be a good choice - if they produce 12V and don't try to drive a constant current.
Will do the study. Very interesting.
12V is also not a must. We only need to adjust the chain length.
All mining devices try to draw constant current anyway, so if they try to drive constant current it's also OK.