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

Here is Why You Need An Adapter

The outlet and plug type used in Denmark are C, E, F and K and in Åland Islands are C and F. This is how they look like.

Åland Islands

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

Type C

Type F

Denmark

In Denmark, outlets of type C, E, F and K are in use.

Type C

Type E

Type F

Type K