Lets say this rating is 12 amps. If the computer and monitor take 2 amps, and the laser printer 10 amps, then the 12 amps could be met or exceeded. Then an internal circuit breaker (in the UPS) could have tripped.
That's why engineers exist. A 15 amp breaker may take 2 hours before it trips on a 20 amp load. We dumb numbers down. For example, we provide a ballpark number to associate a 14 gauge wire with a 15 amp breaker; a 12 gauge wire with a 20 amp breaker.
Turn five 100 watt incandescent bulbs on at the same time on a 15 amp circuit. How much do they demand on power on? Maybe 30 amps. Why does that not trip a 15 amp breaker? Electrical concepts say why. We dumb it down. Five 100 watt bulbs consume 4.2 amps continuously. We just forget to mention the initial 30 amp consumption is normal for a 15 amp breaker and 14 gauge wire. Discussing such details confuse layman.
We know why a UPS is not recommended for a laser printer (obviously not to be confused with an inkjet printer). Motorized appliances do not like the 'dirty' power provided by a typical UPS in battery backup mode.
Even noise could have tripped that UPS into battery backup mode. Then the UPS discovered its battery was defective in about 2 seconds. So it locked out all power - crashing your computer. No circuit breaker need be involved since other electronic circuits can cause the resulting power off and Alarm.
What would happen if five 100 watt bulbs were powered from surge protected outlets? A resulting maybe 28 amp demand would not trip any circuit breaker.
We know a UPS powering a motorized appliance is not recommended because UPS power can be so 'dirty'. Not undersized (insufficient wattage). 'Dirty' power is ideal for electronics and potentially harmful to motorize appliances and power strip protectors. Reality is always this much more complex.
