Question

what if output of an ac to dc convert is shorted

Answer 1

If the wall adapter is just a transformer and rectifier, it is very likely that the transformer winding wire size was chosen to provide sufficient internal resistance to prevent the output short circuit current from causing any immediate damage to the transformer. There may also be an internal resistor to limit the maximum charging current, which will also limit the short-circuit current. If left in a shorted condition very long, the transformer could possibly (but very unlikely) overheat, melt the wire insulation and eventually connect part of the primary winding to the secondary winding, thereby possibly exposing you to the wall plug voltage. However you would have been warned of that by the unit getting hot and smelling bad, like something was burning. If the wall adapter also contains a voltage regulator chip, then the unit will probably have been designed to limit the output current to safely avoid damage to the transformer and regulator chip. This makes it pretty much impossible for you could overheat the transformer sufficiently to cause a primary-to-secondary short and hazard. As for your experiment of electrolysis of water, that is a fun experiment. (I assume you are not planning to make large quantities of hydrogen and oxygen, which could be dangerous -- we breathe oxygen but hydrogen will burn in air, and really well in the oxygen. The amount you can make in a test tube experiment would be harmless.) It would be good to get an inexpensive multimeter (Radio Shack) to monitor the current flow. If the current is too high, move the electrodes further apart. You can also limit the current by putting a flashlight bulb or automotive lamp (tail light or turn signal) in series. Choose one designed to operate at the output voltage of the wall charger and you can be sure you will not burn out the lamp. This is basically a resistor but has the advantage that it it is a low ohm resistor at low currents but higher resistance at higher currents (higher filament temperature) and also that it will roughly indicate the current level by lighting up. Have fun, but be wary of burning smells.

Hope this will help you.... ✌