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

Here is Why You Need An Adapter

The outlet and plug type used in Sierra Leone are D and G and in Greenland are C, E, F and K. This is how they look like.

Greenland

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

Type C

Type E

Type F

Type K

Sierra Leone

In Sierra Leone, outlets of type D and G are in use.

Type D

Type G