You Do Need power plug adapter while traveling from Cape Verde 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 Cape Verde are C and F. This is how they look like.

Cape Verde

In Cape Verde, outlets of type C and F are in use.

Type C

Type F

Sierra Leone

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

Type D

Type G