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

Here is Why You Need An Adapter

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

Madeira

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

Type C

Type F

Namibia

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

Type D

Type M