The current from the wall is AC ~120 volts, the computer runs on DC ~12-20 volts this is what the power adapter does, it turns AC to DC and lowers the voltage to whatever the computer uses.
The inverter drives the back light, the back light (fluorescent bulbs) require high voltage power somewhere around 1000 volts, the laptop power adapter only outputs somewhere between 12 volts and 20 volts (most newer laptops are 19-19.5 volts). The inverter in laptops increase the voltage so the fluorescent bulbs will work correctly.
Newer laptops do not require a inverter because they use LED back lights, the LED back lights do not require high voltage current.
Edited by zingo156, 05 May 2014 - 01:35 PM.