You Do Need power plug adapter while traveling from Denmark to Sri Lanka.

Here is Why You Need An Adapter

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

Denmark

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

Type C

Type E

Type F

Type K

Sri Lanka

In Sri Lanka, outlets of type G are in use.

Type G