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

Here is Why You Need An Adapter

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

Saint Martin

In Saint Martin, outlets of type C and E are in use.

Type C

Type E

Namibia

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

Type D

Type M