Miller made machine, painted Acklands Creamsicle orange. DialArc 250 AC/DC if not mistaken.
Acklands may have had other suppliers, but if you take the serial number and punch it in the search box on the Miller website, like as not you get to pick out from a bunch of manuals.
I have an Acklands labeled and painted 225D Bobcat, that I like a LOT!
And in all seriousness, no matter who made this one, at the price, it's cheaper than buying the (not so commonly available any more) surplus diodes and doing your own DC conversion on a Tombstone or similar AC only rig!
Were it mine, i think I would convert from the Miller taper connectors to one of the twist lock types out there, but that would depend on what comes with for cables, if any.