Basic wall wart ps but awkward V for replacement, just died, not been left
on or abused .
Rated 115 deg C ,3A in the primary side, In use about 30mA of mains.
I don't think I've sliced into one before and am not sure what I would
expect if fused from overtemp or old-age etc.
Probably as all the body of the fuse would be at the same over-temperature
then all the Woods metal/ high bismuth/antimony solder or whatever, would
have all melted and coalesced into one lump or a lump either side , would
have been my guess.
If failed from current surge/ old age / shock/vibration/ chemical breakdown
or something then a tiny fracture or a change of texture to powder or
something , instead of shiny metal.
Looking under x30 mag
This one between the terminal wires about 3mm run of the low temp metal with
about 0.5mm gap on one side, the end of shiney "fuse-wire" run rounded as
though locally melted , all in its original posistion with no obvious
channel in the casing to mechanically retain it in place.

So not really any more forward on failure modes of these fuses.