Why would any dealer say anything is covered under warranty until they diagnose it?
The EVSE is covered under the Voltec warranty. GM does not communicate the Voltec warranty items well with GM dealers.
If you are getting the 'blown fuse' thing, it's an issue with where you are plugging in and/or the electrical configuration at that site, GM is under no obligation to replace the EVSE under warranty in that case. Many, however, do as a goodwill gesture.