You Do Need power plug adapter while traveling from Costa Rica 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 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

Sierra Leone

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

Type D

Type G