I have nothing but good experience with Cyberpower UPS’s.
Whenever they kick in, everything continues to function as normal.
Maybe it’s that American Electricity.....
Well, I'll tell the story and see if you think a different conclusion is warranted. One day about a year ago I was using my Mac Pro, and realized that the power supply for the backup disk that I wanted to use wouldn't fit on the power strip, because the orientation of the pins would interfere with an adjacent power plug. "No problem," I thought, "I'll just re-arrange the plugs on the fly because my Mac and its monitor are powered through the CyberPower UPS. The display shows five bars of capacity, so it certainly should be able to supply the juice for the ten seconds it will require to unplug the CyberPower's plug and move it to accommodate the backup disk's power supply." So I unplug the CyberPower UPS, it starts beeping as expected, but to my horror I look up at it and see that the battery level on the display is now showing completely depleted - zero bars! And then before I can even get it plugged in again I hear a longer, strangled beep and all of the devices plugged into the UPS shut off abruptly. The UPS was about two years old at that point.
So I move the power plugs as needed, reboot the Mac, and now the 23" Cinema display won't come up - it shows a dark screen and the funny blinking sequence on the status LED. My 24" LED Cinema display still works, so I limp along with that. After searching the Internet I find that the likely cause is that the 3.3 voltage regulator is blown on the 23" display.
So, the only adverse electrical event between the period when the display worked five minutes before, and its current non-functional condition is that the CyberPower UPS tried to bridge a power outage with a dead battery. My guess is that the unit lost AC output regulation in that last gasp of trying to power the load with the dead battery, and sent a spike of voltage into the loads. It's worth noting that the reason that CyberPower units are cheaper than the competing APC units is because they don't offer over-voltage regulation - with an APC unit (or at least some APC units) if the incoming AC is above line level the APC UPS will down-regulate it to an acceptable output voltage.
To be fair, there were other instances of short power outages where the CyberPower unit carried the load across the outage without incident. But it's unforgivable that the unit would cause damage as a result of the fairly common experience of battery depletion - all batteries eventually die, and since the unit doesn't provide any advance warning about the true state of the battery, one runs a substantial risk in continuing to use a CyberPower UPS.