Sri Lanka uses a voltage of 230v and a frequency of 50Hz. So if you are from a country that use 110v range please make sure your equipment can work under 230v. Otherwise you will need to bring a suitable voltage converter.
Sri Lanka used to have Type D plugs but recently started using Type G (Similar to the one used in the UK). So most old buildings still have Type D sockets, so it is hard to predict which type of socket will be available. So it is advisable to keep adapters to support both types.