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

Here is Why You Need An Adapter

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

Brazil

In Brazil, outlets of type C and N are in use.

Type C

Type N

Swaziland

In Swaziland, outlets of type M are in use.

Type M