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

Here is Why You Need An Adapter

The outlet and plug type used in South Sudan are C and D 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

South Sudan

In South Sudan, outlets of type C and D are in use.

Type C

Type D