What is the voltage in Germany?

The voltage is 220 volts .... but that isn't a complete answer. What kind of "certain plug-in appliances" are you talking about? A plug adapter will work for a battery charger or laptop PC, but if the device has an electric motor you will need something that will also change the AC frequency from 50 to 60 hertz.

The voltage is 220 and the prongs are round. To know if you just need an adaptor or a transformer, you have to look at the appliance. Most hair dryers and curling irons have writing on their side telling what volt (V), wattage (W), and Hertz (Hz) they use. (other things may have this info on a tag on the electrical cord or elsewhere on the appliance) If it says 110/220 or "dual voltage" then it will work with just an adaptor (usually a small round plug or small black one) that accepts the flat american prongs and has round prongs.

If it only says 110, you need a transformer. These are usually heavy and expensive. Transformers are rated by watts and you need to get one that can handle as many watts as your appliance requires.

American clocks will not work, even with a transformer. Something about the electric cycle differences prevent them from keeping time correctly.

220

220/230 volts AC 50 hertz (cycles per second)

JUST ******* GOOGLE IT!