Made by one of the leading manufacturers in the industry, the Air star Series step up / step down voltage transformers offer you a safe, reliable, affordable and convenient solution to converting voltages from 110-120 volts up to 220-240 volts, or from 220-240 volts down to 110-120 volts for both home use and industrial applications. The ST-500 is rated at 500 watts maximum. It features a heavy-duty cord with a standard round prong plug plus a free American Flat outlet plug adapter. There are a total of two outputs on the front panel. Some items, such as laser printers and power tools spike when you turn them on. For these types of situations you need to buy a transformer that is at least 3 times the items capacity. UseAmps to calculate Watts: Volts (times) Amps=WattsFor example 110Vx 5A = 550W