You Do Need power plug adapter while traveling from Saint Helena to Mozambique.

Here is Why You Need An Adapter

The outlet and plug type used in Mozambique are C, F and M and in Saint Helena is G. This is how they look like.

Saint Helena

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

Type G

Mozambique

In Mozambique, outlets of type C, F and M are in use.

Type C

Type F

Type M