Sri Lanka has 230-240 volt, 50-hertz alternating current. Continental European plugs fit in the ungrounded sockets, although you may have to give them a push. There are also 3 pin sockets. Sometimes, hotel receptions will have adapter plugs.
Power-cuts are frequent. Hotels always stock candles or oil lamps, but it is a good idea to bring a good torch for evening walks. The many holes, bumps and ditches in and along the roads can become dangerous when street lighting stops working.