Ebay, used computer or telecom supplies.
Usually 48 - 52V, and a few KW is quite common.
There is a 48V HP server supply that is rated for 3KW, and usually goes
for $50 or so that pretty much always seems to be available, or
(usually) various options taken from redundant cell site 'rectifier
shelves' that will do what you need.
The HP supplies suffer from being VERY deep, being designed for server
racks, but if you can live with that it is a cheap way to lots of DC.
The ex cellphone stuff is nice as it often has connections for load
sharing so you can parallel a few for heavy loads.
The cell phone base stuff may also be better about EMC then the computer
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