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

Here is Why You Need An Adapter

The outlet and plug type used in Swaziland is M and in Nigeria are D and G. This is how they look like.

Nigeria

In Nigeria, outlets of type D and G are in use.

Type D

Type G

Swaziland

In Swaziland, outlets of type M are in use.

Type M