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

Here is Why You Need An Adapter

The outlet and plug type used in Åland Islands are C and F 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

Åland Islands

In Åland Islands, outlets of type C and F are in use.

Type C

Type F