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

Here is Why You Need An Adapter

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

Vanuatu

In Vanuatu, 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