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

Here is Why You Need An Adapter

The outlet and plug type used in Belgium are C and E 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

Belgium

In Belgium, outlets of type C and E are in use.

Type C

Type E