A fuse which is operating close to its rating may fail of its own accord due to aging or the fuse may simply have been defective from the start.
LED lamps which are intended to operate from 12 volts d.c may have a problem with a 12 volt halogen power supply. Low voltage halogen power supplies are usuaqlly just a transformer providing a.c. voltage. First, the LED current draw will be significantly less and the power supply normally compensates for higher current by providing a slightly higher no load voltage. Add to this that the peak voltage will be 1.414 times the rms voltage so the voltage that the LED experiences could be in the mid twenty voltage range. This voltage may exceed the maximum reverse voltage rating which may destroy the LED's as they typically have a maximum 5 volt reverse voltage rating per LED.
Secondly, the operating range of a white LED is between 3.0 and 3.5 volts. 12 volt LED's usually have three LED's in series for 1`0.5 volt plus a current limiting resistor to drop the voltage for 12 to 10.5, more or less. If the rms voltage of the transformer is 15 volts, the LED current would be about three times what it would be at 12 volts. The LED's will burn brighter but with a significantly reduced life.
Lastly, since LED's have a fairly rapid turn on and off, you may experience a faint 60 hz flicker.