Hey guys,

I understand the 277V L-N voltage is too high for most (all?) PSU's, what is the best way to use this power source for mining? Must I go with a step-down transformer?

THX

^^ ditto.
Just place the delta/wye step down xmfrs at the end of each aisle along with their required distribution breaker panels and feed each xmfr with a run from the 480V main panel feeding the delta side. Makes it nice and safe/easy to work on each aisle plus saves on wire cost by keeping the 208v runs needing really thick wires that run only the length of the aisles. Also since the miners are now directly fed from across the phases the is no need for a Neutral wire for either the 480v side nor the wye 208v side (but ground does connect to the center of the wye).

One trick to do is set the taps on the 480/208V transformers to produce higher voltage. Usually you can set up to around 215-220v and that give a little extra margin to work with when the line dips.

415v line is along ways from 480. No matter what a step down xmfr is needed so they might as well do it right.