Some lights blow fuse, others dim, afterwards polarity mixup

Reversing polarity in a dimming circuit is a nyet nyet. The dimmer takes an even dimmer view of being polarity ambushed. When the circuit throws a tantrum it causes the entire power circuit to do a brownout.

Diodes unless they fry, block voltage in one direction.

Replace the dimmer circuit then see what you have. 555 timer circuit are also reverse polarity short-tempered. Most DC stuff complains bitterly in fact.