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

Here is Why You Need An Adapter

The outlet and plug type used in Guinea are C, F and K and in Solomon Islands are G and I. This is how they look like.

Solomon Islands

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

Type G

Type I

Guinea

In Guinea, outlets of type C, F and K are in use.

Type C

Type F

Type K