You Do Need power plug adapter while traveling from Costa Rica 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 Costa Rica are A and B. This is how they look like.

Costa Rica

In Costa Rica, outlets of type A and B are in use.

Type A

Type B

Solomon Islands

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

Type G

Type I