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· What is Off-line UPS 

The operation mode of Off-line UPS: When the electricity supply is normal, it will directly supply to the load to use. When the inverter doesn’t work, one pass by will charge battery pack through charging circuit; when the electricity voltage is unstable or an exception occurs, UPS will switch to the internal converter from the converter to provide stable power to the load to use, the majority of the wave of these products are square wave or ladder waves, which also apply to the computer's power supply.