Some adapters are more problematic than others. For example if the charger and the vehicle both expect the other side to initiate the charging process and withhold power until some voltage is detected then the adapter may need its own independent power supply to jump-start the charging process. Locks are another problem—some combinations would require the adapter to provide powered locking mechanisms for both sides. None of this makes an adapter impossible, but it could be too expensive or unwieldy to be a practical solution.