Most Lionel accessories,even post war will work on DC with the exception of those with vibrator motors. For those they actually work better on half waved pulsed DC accomplished by a single diode in series to it . If running other type PW on DC such as the semaphore reduce the voltage until the accessory just works,then add a few volts. Too much DC voltage can overheat them,
For more modern accessories with bridge rectifiers in them,it does not matter if DC is applied.
Dale H