Why Air Conditioner's voltage stabilizer shows bizarre approach to the desired voltage?
The voltage stabilizer mostly iikely uses an autotransformer to step the voltage up and down.

It automatically switched between the taps, so it uses one tap for stepping up from 190-195 to 235-240 (the same tap would step up from 178 to 220). Then, once the voltage gets high enough, it switches to another tap for stepping up from 200 to 210. Finally, nce the voltage gets high enough (215), the autotransformer is switched off and the input is passed trough straight.

This is cheaper than double conversion (convert AC to DC, then back to AC at the correct voltage) and is good enough if the load can tolerate slightly different voltages.

Line Interactive UPSs with AVR have the same voltage stabilization - straight, step down by 10% or step up by 10%. If stepping up or down results in the voltage still out of spec, the UPS switched to battery.