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

Here is Why You Need An Adapter

The outlet and plug type used in South Africa are C, M and N and in Guatemala are A and B. This is how they look like.

Guatemala

In Guatemala, outlets of type A and B are in use.

Type A

Type B

South Africa

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

Type C

Type M

Type N