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

Here is Why You Need An Adapter

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

Eritrea

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

Type C

Type L

Slovenia

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

Type C

Type F