What is wrong with the your unit is there is likely a transistor that does not have isolation to case. Safe systems ground case, to provide safety, and improve tolerance to EMI. There could be 450V or more there, and could be lethal. They might get by UL, because it is a 12V supply, that is not good. Rubber isolators are for vibration, not electrical isolation, most rubber has carbon, other fillers and is conductive. Remember those snake fire works, seen rubber do that when improperly used in power circuits.
