Laser printers plugged into UPS's aren't great (and then there was my previous boss who destroyed a pretty large unit by repeatedly boiling a kettle from it du

Laser printers plugged into UPS's aren't great (and then there was my previous boss who destroyed a pretty large unit by repeatedly boiling a kettle from it during a power cut), but it's worth pointing out that the OP had his laser plugged into the same circuit as the UPS but not onto the battery - I took that to mean it's on the same radial/ring/breaker rather than connected to the UPS at all. I'm guessing the surge current to the laser was causing the UPS to register a brownout and potentially not behave correctly at that point.