Electricity in Switzerland is 230 V, 50 Hz AC. Plug sockets are round and take three round pins - they can take Europlugs with two pins. If you are coming from the US, the UK or Ireland you definitely need an adaptor - as well as from many other countries. Travellers from the US (and other countries with a a different voltage than 230 V) additionally need a voltage converter. In modern hotels you might find multi-use sockets. Otherwise ask for an adaptor at the reception or buy one in a traveller's or electronics shop (main station).