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

Here is Why You Need An Adapter

The outlet and plug type used in Sierra Leone are D and G 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

Sierra Leone

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

Type D

Type G