Portable generators are either conventional or inverter. Conventional generators use a mechanical alternator to produce AC power while inverter generators produce DC power and convert it to AC power using digital electronics. Inverter generators are smaller and lighter but more expensive.
Conventional generators run at a constant 3600 RPMs while inverter generators can run at variable speeds depending on the electrical demand. This allows inverter generators to run at slower speeds much of the time, which saves fuel and reduces noise.
Inverter generators usually produce cleaner power with a total harmonic distortion of less than 5% while conventional are capable of greater output and extended run times.