The grid in South Sudan works at 230 V and 50 Hz; the recorded sockets are Types C, D and G. At 230 V the supply matches what UK and European appliances expect, so no converter is needed.
The same socket system is used in Sudan, so one adapter covers all of them. Watch out when moving on: Lesotho and Botswana use a completely different system. In Africa, 2 of 55 recorded destinations use exactly this combination.
Protective earth
Grounded and ungrounded sockets may occur
South Sudan has sockets with a protective earth (Types D and G) and without (Type C). A plug that fits mechanically does not guarantee earthing.