Also known as a varlac, this device allows you to adjust the input voltage to the product you are testing. If you don't need frequency adjustment, this is a much lower cost alternative to a power source. Output is fused. Single phase units noted below, 3 phase units available. Standard models include input voltages from 120VAC to 480VAC. Frequencies to 2000 Hz can be accommodated. Special units for voltages to 1000 VAC are available.