If, contrary to the expectations, the device should not work properly, the most common cause is a burntout fuse. In the case of the World Adapters and as well the Country Adapters for Switzerland and the UK you have the facility to simply change the fuse yourself. Spare fuses are available at electronics retailers and many online stores.

To do this, simply take a screwdriver, a coin or something similar, place it in the slot on the bottom of the device and turn it lightly anticlockwise. Now place a fuse of the appropriate size in the holder and fix it into the adapter again. (United Kingdom: flip closure, simple to open with a screwdriver).

Required fuses:
World Adapters of the series EVO, MUV, Classic: Slow Blow Microfuse T2.5A 250V AC
World Adapters of the series PRO: Slow Blow Microfuse T10A 250 V AC
Country Adapters Switzerland: Slow Blow Microfuse T10A 250 V AC
Country Adapters UK: Slow Blow Microfuse T13A 250 V AC