You Do Need power plug adapter while traveling from Saint Lucia to South Sudan.

Here is Why You Need An Adapter

The outlet and plug type used in South Sudan are C and D and in Saint Lucia is G. This is how they look like.

Saint Lucia

In Saint Lucia, outlets of type G are in use.

Type G

South Sudan

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

Type C

Type D