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

Here is Why You Need An Adapter

The outlet and plug type used in Eritrea are C and L 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

Eritrea

In Eritrea, outlets of type C and L are in use.

Type C

Type L