First you must know that most American appliances are designed to run off of 110 volts and Most German appliances are designed to run off of 220 volts.
This means that if you plug an American stereo, razor, computer, etc into a German outlet it will destroy it!!
The prongs are different so it is hard to make this mistake but outlet adapters are sold and this does happen often. The reason the adapters are sold is because some American appliances are Dual-Voltage and can run off of 110 or 220.
To find out if your appliance is Dual-Voltage you must look at the power information on the appliance, either on the appliance itself or on the power box on the cord. If you still haven?t found the information refer to your user manual. If your appliance is not dual voltage the only option you have in order to use it in Germany is to purchase a power converter.
Power converters can be purchased on the world-wide web (of course), or select appliance and hardware stores. If you are somehow allowed access to a U.S. Army base in Germany, you can purchase one at the Post Exchange.
When selecting your power converter be sure that it is converting 220 volts to 110 volts and not the other way around.
Next, you need to select the size of the power converter in which you will need for your device(s) this should be relatively self explanatory.
Check the power output of the device and be sure it is equal to or below, below is recommended, the voltage of the converter.
Using certain clocks/alarm clocks can run slower or faster than usual even if the clock is dual-voltage. The only way to avoid this is to be sure the clock is of good quality and relatively new. If the clock is plugged into a power converter this should not be an issue.