Headlights go out dashboard turns off car still drives.

Had the car in the dealership because a brake light was off. Was told it was a switch in the master cylinder so they replaced it. I get the car back and after 2-3 days I was driving to work in the dark when all of a sudden the head lights shutoff, then the dashboard including every gauge including heat, radio, external temperature go out. The radio and heater still worked but all lights and indicators were out. Then the lights would come on, and the dashboard seemed to reboot and come back to life. This happened repeatedly my entire ride to work. I took it back to the dealership and they said the alternator was bad; but couldn't diagnose any other issue. Had the alternator replaced. Thought that would take care of the problem but it didn't. The flashing of the light doesn't occur repeated like it did before but it still happened. The battery light comes on and the dashboard and headlights may or may not go off. I've had both the battery and alternator checked and I am told they are good. The battery is an 850 ah output and it was putting out around 825 when tested. The battery is under warranty but the guy said it wasn't bad.

I cannot afford another car so I'm hoping someone on this forum can help with this.

Thank you.