You Do Need power plug adapter while traveling from Swaziland to Cameroon.

Here is Why You Need An Adapter

The outlet and plug type used in Cameroon are C and E and in Swaziland is M. This is how they look like.

Swaziland

In Swaziland, outlets of type M are in use.

Type M

Cameroon

In Cameroon, outlets of type C and E are in use.

Type C

Type E