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?
4 Answers
Check whether your electrical system is 220V/50Hz or 240V/50Hz, and compare the UPS output waveform and regulation specifications. A 1200VA rating does not necessarily mean it can comfortably handle a gaming desktop, and 650W can be marginal depending on the graphics card and power spikes. A UPS with enough wattage headroom and pure sine-wave output would be the safer choice.
No, the buzzing is not considered normal. It could be related to a failing UPS battery, an overloaded unit, or the stepped/approximated waveform produced by some entry-level UPS models. If the UPS is still under warranty, contact the seller or manufacturer. Otherwise, disconnect the PC from it and replace it rather than risking instability or damage.
A buzzing power supply while connected to the UPS is not something to ignore. The exact UPS model, your PC’s power supply rating, the computer’s components, and anything else connected to the UPS all matter. A 650W UPS may also have a much lower practical capacity than your PC’s peak demand. If it is overloaded or producing a rough simulated sine wave, the PSU can buzz or behave poorly. I would avoid using it until you confirm the load and UPS specifications, and consider a higher-capacity pure-sine-wave UPS.
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?
The sound definitely seems to come from the PC’s power supply, not from the UPS itself.