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

Here is Why You Need An Adapter

The outlet and plug type used in Swaziland is M and in Nepal are C, D and M. This is how they look like.

Nepal

In Nepal, outlets of type C, D and M are in use.

Type C

Type D

Type M

Swaziland

In Swaziland, outlets of type M are in use.

Type M