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

Here is Why You Need An Adapter

The outlet and plug type used in Sierra Leone are D and G and in French Guiana are C, D and E. This is how they look like.

French Guiana

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

Type C

Type D

Type E

Sierra Leone

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

Type D

Type G