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

Here is Why You Need An Adapter

The outlet and plug type used in Saint Lucia is G and in South Africa are C, M and N. This is how they look like.

South Africa

In South Africa, outlets of type C, M and N are in use.

Type C

Type M

Type N

Saint Lucia

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

Type G