You Do Need power plug adapter while traveling from South Sudan 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 South Sudan are C and D. This is how they look like.

South Sudan

In South Sudan, outlets of type C and D are in use.

Type C

Type D

Sierra Leone

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

Type D

Type G