Pure (or “true”) sine-wave output is the highest quality output available. When utility power is present, all APS inverter/chargers provide connected equipment with the pure sine wave that the utility company generates. However, when utility power is absent (during a power failure), and the inverter/charger switches to a battery source, only APSX3024SW and APSX6048VR models will continue to provide connected equipment with pure sine-wave output. All other models provide a pulse width modified (PWM) sine wave. While PWM sine wave output is perfect for the majority of applications, sensitive computers and telecom equipment may require the premium output that only the APSX3024SW and APSX6048VR can provide.