You Do Need power plug adapter while traveling from Brunei 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 Brunei is G. This is how they look like.

Brunei

In Brunei, outlets of type G are in use.

Type G

French Guiana

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

Type C

Type D

Type E