'15 charger alternator issue

I've seen those alternators intermittently have brushes stick, and have issues (if equipped) with the over-running clutches- though I can't remember if your car would have one - I'm thinking it does not. Most likely the brushes were stuck, and when they finally loosened and made contact, the squeal you heard was from the alternator being under load. The loss of sub systems is a completely normal operation, when enough voltage is lost. It is a designed in feature, to conserve as much battery as possible. If it happens again, try knocking the alternator housing with a hammer or rock or similar. The idea is to just jar it enough to dislodge the brushes, not beat the crap out of it. Ideally, though - I would replace the alternator.