It's true for both, and you could prove it to yourself if you had one in your lap. It's also the concept behind electrical braking and regenerative braking as used in leccy cars. A modern car alternator can output an easy - what? - 100 amps if required. (Headlamps, driving lamps, heated screen, wipers, heater fan, flat battery etc). If you place that 100A leccy load on it, it'll deliver it. That's a fair amount of power, and it's being provided ultimately by an extra load on the engine and therefore by the car's fuel. You can try this - let your car idle, and then switch on all of the above. You will almost certainly hear the additional load that's been placed on the engine. Mr Ha - do you think that the alternator is always placing that load on the engine, even when none of these items are on and the battery is fully charged?