You Do Need power plug adapter while traveling from Lesotho to Mauritania.

Here is Why You Need An Adapter

The outlet and plug type used in Mauritania is C and in Lesotho is M. This is how they look like.

Lesotho

In Lesotho, outlets of type M are in use.

Type M

Mauritania

In Mauritania, outlets of type C are in use.

Type C