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 convertor. The best place to pick these up is at home, though if you arrive without one try your hotel concierge or reception; they should be able to point you to the nearest electrical store if they fail to provide a convertor themselves.