The electrical voltage delivered via power outlets varies in different parts of the world. Some places, such as Japan, have a mains power voltage as little as 100V, while others, such as Kenya, have a mains power voltage as high as 240V. This means that when you wish to use a device from one country in another country's power outlets, you need to check the voltage of that country to ensure it is safe to use with your device.
Some appliances are compatible with multiple voltages, while others are built to work specifically with one voltage. To find out if your appliance is one of them, check the appliance label and/or instruction booklet. Some examples of appliance labels are below:
If your device is compatible with the voltage used in the country you are visiting, then a plug socket adaptor may be all you need (assuming there is a difference between the plug type as well). Otherwise, if your device is not compatible with the voltage used in the country you are visiting, you will need to also use a Transformer to transform the voltage so it is safe to use your device.