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

Here is Why You Need An Adapter

The outlet and plug type used in French Guiana are C, D and E 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

French Guiana

In French Guiana, outlets of type C, D and E are in use.

Type C

Type D

Type E