how do they change an AC current to a DC current?
AC to DC is easy, you bring down the voltage with a transformer, and you rectify the current with Diodes, mostly a diode bridge which is a collection of 4 diodes to split the Negative from the Positive current. A Capacitor will than sit between the Positive and the Negative to flatten the current to DC which is like a straight line of current, unlike the AC which is like waves. DC to AC requires the opposite conversion which is more complicated, to make a straight line current (DC) into Waves current (AC) and then use a transformer to increase it from say an originally car battery power of 12V now modified to AC and into to 230 V AC for normal use. AC to DC usually provides more amps on DC while to go DC to AC provides less Amps on the AC than what it pulls from the battery in DC. Hope this clarifies things a bit better.
