But what's the breaking capacity at 250 VDC (primary side of an SMPS), or even at 48 VDC (UPS battery pack)?
Strictly speaking, these glass fuses are not designed to interrupt DC circuits and shouldn't be used in multimeters. They have no DC voltage interrupt certification.
It doesn't mean that they can't interrupt some DC voltages safely, but there is no way of knowing without conducting specific tests on the circuit under consideration.
At best, with fast acting fuses (F/FF), a reduction of 25% of rated voltage is to be expected, depending on circuit inductance time constant.
To err on the safe side, I wouldn't use them in multimeters to test circuits with DC voltages higher than 30VDC.
'There is a limit as to how much arc energy a fuse can absorb. The DC voltage rating of a fuse always has an associated time constant because both terms are needed to define how much arc energy the fuse can absorb. For fuses, the DC voltage rating is inversely proportional to the time constant. In other words, as the time constant of the circuit increases, the voltage capability of the fuse decreases.'