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

Here is Why You Need An Adapter

The outlet and plug type used in Eritrea are C and L 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

Eritrea

In Eritrea, outlets of type C and L are in use.

Type C

Type L