You Do Need power plug adapter while traveling from Sierra Leone 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 Sierra Leone are D and G. This is how they look like.

Sierra Leone

In Sierra Leone, outlets of type D and G are in use.

Type D

Type G

Solomon Islands

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

Type G

Type I