How do I know whether a fuse is a DC fuse or an AC fuse?
The key difference between a fuse's AC voltage rating and its DC voltage rating is a question of being able to stop the arc that forms when the fuse blows. DC arcs are much harder to stop than AC arcs, so you'll regularly see fuses that are rated for, say, 250VAC but only 32VDC.

Often, you'll find that fuses specifically intended for DC applications have a small spring inside that helps pull the ends apart when the element melts.