Oh sorry ! it's automatic power system*..briefly..it's a transformer that trasforms 12 volts to 220 volts .we use it when the electricity is off..
so when electicity is on, the 12volts battery charges.and when the electricity cuts off,we turn the APS on ( or maybe automatically) to get the 220 volts (by transforming the 12 volts)...
of course,the APS delivered power is not big.so we can't turn on much electrical devices upon using it.
thank you