[AFMUG] Dc power supply + solar controller for cheap dc ups?

[TJ Trout]

What do I need besides a dc power supply to be able to have a dc ups with
the ability to charge batteries and have seemless transfer to and from
batteries when ac fails as well as limiting on the batteries being charged
so the charging doesn't over run the current of the psu once the ac comes
back ? Aka poor man's ups? Dell nps700ab poweredge supplies are 12v 700w
for like 5 bucks