You Do Need power plug adapter while traveling from Pitcairn Islands 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 Pitcairn Islands is I. This is how they look like.

Pitcairn Islands

In Pitcairn Islands, outlets of type I are in use.

Type I

French Guiana

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

Type C

Type D

Type E