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

Here is Why You Need An Adapter

The outlet and plug type used in Niger are C, D, E and F and in Namibia are D and M. This is how they look like.

Namibia

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

Type D

Type M

Niger

In Niger, outlets of type C, D, E and F are in use.

Type C

Type D

Type E

Type F