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

Here is Why You Need An Adapter

The outlet and plug type used in Guinea are C, F and K 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

Guinea

In Guinea, outlets of type C, F and K are in use.

Type C

Type F

Type K