Electric shock with external supply

Hello everybody,

recently I bought the LCD keypad shield (1602) for my arduino UNO. My USB-port couldn't deliver enough power so the shield wasn't working. Therefore I looked for an external supply today. I found a 12V AC/DC supply that I connected to the arduino. Immediatly the LCD started to work fine, but I got electric shocks from the arduino and the shield. Could this be the problem of my adapter, or is the shield just not working as it should?

Stop using the adapter now. After that you can read the rest of this. There are many kinds of shocks. Some power supplies may leak a little, which is harmless, or they can be dangerous if they are for instance broken. Try to return your power supply and buy a new one. That is safest way.

It would be a miracle if some kind of Arduino Shield would give you electric shocks. Those that I know of, do not generate high enough voltages to give el. shocks.

It is possible that the power supply of your computer leaks a little electricity or is broken, but you would notice it without the adapter too. If you touch metal parts of your computer you may notice something, it depends what kind of mains plugs and cables you have.

EDIT: Fixed some typos.