You Do Need power plug adapter while traveling from Nauru 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 Nauru is I. This is how they look like.

Nauru

In Nauru, outlets of type I are in use.

Type I

Åland Islands

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

Type C

Type F