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

Here is Why You Need An Adapter

The outlet and plug type used in Monaco are C, E 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

Monaco

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

Type C

Type E

Type F