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

Here is Why You Need An Adapter

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

Mauritania

In Mauritania, outlets of type C are in use.

Type C

Namibia

In Namibia, outlets of type D and M are in use.

Type D

Type M