Electricity in Poland is 230V, 50Hz AC. Plug sockets are round with two round-pin sockets. Therefore if you are coming from the US, UK or Ireland you are definitely going to need a plug converter. The best place to pick these up is at home though if you do arrive without a converter try your luck at the airport or with your hotel reception; they should be able to point you to an electrical store if they can't provide a converter themselves.