You Do Need power plug adapter while traveling from Eritrea 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 Eritrea are C and L. This is how they look like.

Eritrea

In Eritrea, outlets of type C and L are in use.

Type C

Type L

Denmark

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

Type C

Type E

Type F

Type K