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

Here is Why You Need An Adapter

The outlet and plug type used in Namibia are D and M and in Norfolk Island is I. This is how they look like.

Norfolk Island

In Norfolk Island, outlets of type I are in use.

Type I

Namibia

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

Type D

Type M