You Do Need power plug adapter while traveling from Tuvalu 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 Tuvalu is I. This is how they look like.

Tuvalu

In Tuvalu, outlets of type I are in use.

Type I

South Africa

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

Type C

Type M

Type N