5.6. Why cannot my small-power-consumption device get power from the UPS when mains is off?
When selecting UPS, we consider two key factors, the output power and backup time, to make sure the UPS has enough power to supply to the load and enough backup time when mains goes off. Besides of these two factors, to consider the waveform of the UPS output is worthy, especially when your loads are modern, advanced and/or accurate. In these years, power efficiency is concerned more and more, and new technology to improve efficiency is adopted accordingly, active PFC is one of them. Many servers and high-end PC use power supplies with active PFC. Then these devices are better to connect to pure sine wave UPS. The device with active PFC might still work when connecting to non-pure sine wave UPS if it consumes much lower power than the UPS can supply. But when it increases the load, the active PFC circuit might force the UPS to protection mode (that is to turn off the UPS output) or cause the power supply restart. For the accurate instrument, it’s necessary to use pure sine wave UPS, otherwise, the reading of the instrument might not be as accurate as it should have. Even it looks working but the result is not what you expect.