Electricity in Portugal is 220 Volt, 50Hz. Almost all electronic devices will adapt automatically to the different voltage. If in the labelling of your device says “120V” or “100-120V”, you will need a voltage transformer. If it does not say this, generally your device will adapt automatically.
What you may need is a plug adapter. Sometimes the plugs adapters are combined with voltage transformer. Please read carefully the information on the unit. If the label of your device says “110-220” or “100-240” then you will only need a simple plug adapter (in this case, no transformer needed).
If you need more information on this website you will find more detailed information about electricity and adapters: http://www.power-plugs-sockets.com/
You have to select on the right side of the page where are you travelling, then say which country you live in and you will see all the information.