I think it's safe to say that there's at least one model of 3D printer that works in microgravity -- since one was sent to the International Space Station a few months ago. I presume the one there is an FDM type, as those need not be dependent on gravity; my Ender 3, for instance, has positive drive both ways on all three axes, so as long as the filament source is kept captive, the printer ought to work the same as it would on Earth.
Beyond that, there is the Quinly setup, in which a common FDM printer like the Ender 3 is set up at about a 45 degree angle, using a polymer coated glass bed, to allow network printing part after part (the printer pushes the parts off the cooled bed with the X gantry and hot end housing before preheating for the next print). Similar methods are used to print at a significant angle on a flat build surface for conveyor bed printers that can both print very long parts, and print sequences of parts one after the other (the belt carries the parts to the turn-around, then the flex pops them off).
The operation of common FDM printers depends on mechanical grip of the filament, screw or toothed belt drive of the axes, and adhesion of the first layer to the build surface and of subsequent layers to those already laid down --- this ought to work even upside down, against gravity, at least until the weight of the part starts to compete with its adhesion strength.