My PC runs normally when plugged directly into a wall outlet, but its power supply starts making a buzzing sound when I connect it to an APC UPS rated at 1200VA/650W. The UPS displays an input voltage of about 201V, while my household supply is supposed to be around 220–240V. Is that voltage unusually low, and could the UPS waveform, its capacity, or the low input voltage be causing the buzzing? Is it safe to keep using the PC with this UPS, or could it damage the computer?
1 Answer
About 201V: that is low if your normal supply is nominally 220–240V, although the acceptable range depends on your local electrical standard and how accurate the UPS measurement is. The UPS could have an input-sensing or voltage-regulation problem. Since the buzzing comes from the PC power supply rather than the UPS, I would not assume it is harmless.
Would it be safe to leave the PC connected to the UPS for now, or could the unusual output damage it?