You Do Need power plug adapter while traveling from Sierra Leone 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 Sierra Leone are D and G. This is how they look like.

Sierra Leone

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

Type D

Type G

French Guiana

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

Type C

Type D

Type E