There are three basic types of dc-ac converters depending on their output waveform: square wave, modified sinewave, and pure sine wave . The square wave is the simplest and cheapest type, but nowadays it is practically not used commercially because of low power quality. The modified sine wave topologies (which are actually modified squares) provide square pulses with some dead spots between positive and negative half-cycles. They are suitable for many electronic loads, although their THD is about 25%. Priced in the range of $.05-$0.10 per watt, models that employ such a technique are the most popular low-cost inverters on the consumer market today
A true sinewave inverter produces output with the lowest total harmonic distortion (normally below 3%). It is the most expensive type of AC source, which is used when there is a need for clean sinusoidal output for some sensitive devices such as medical equipment, laser printers, stereos, etc