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

Here is Why You Need An Adapter

The outlet and plug type used in French Guiana are C, D 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

French Guiana

In French Guiana, outlets of type C, D and E are in use.

Type C

Type D

Type E