Before you pack: Mauritania uses Types C and E, 230 V and 50 Hz. At 230 V the supply matches what UK and European appliances expect, so no converter is needed.
You will find identical sockets in Côte d’Ivoire, Madagascar, Gabon and Tunisia. Nearby but different: Ghana, Botswana and Malawi – an adapter for Mauritania will not fit there. 21 of the 55 destinations in Africa share the plug types of Mauritania.
Protective earth
Grounded and ungrounded sockets may occur
Mixed supply: Type C without earth, Type E with earth. Which one is in your room only shows on arrival.