The Apple II power supply is of a switching type that rectifies the AC input voltage to a DC voltage for use internal to the supply. The AC input is first sent through a line filter and then to a diode bridge for rectification. The line filter consists of inductors and capacitors to smooth the waveform of the input voltage. This action would soften the square waves an inverter might supply and the whole combination makes it OK to use an Apple II on a square wave AC supply.
Article Change History:
17 Feb 1997 - Reviewed for technical accuracy, revised formatting.