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

Here is Why You Need An Adapter

The outlet and plug type used in Solomon Islands are G and I 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

Solomon Islands

In Solomon Islands, outlets of type G and I are in use.

Type G

Type I