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

Here is Why You Need An Adapter

The outlet and plug type used in Eritrea are C and L and in Guinea are C, F and K. This is how they look like.

Guinea

In Guinea, outlets of type C, F and K are in use.

Type C

Type F

Type K

Eritrea

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

Type C

Type L