You Do Need power plug adapter while traveling from Sierra Leone to Costa Rica.

Here is Why You Need An Adapter

The outlet and plug type used in Costa Rica are A and B 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

Costa Rica

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

Type A

Type B