An insurance company I worked at had a similar experience, tech showed up to service a UPS unit and was supposed to switch power away from UPS unit while keeping everything else on. Instead they managed to turn off all power to the entire server room. On a Friday. Absolute chaos ensued, staff were summoned back from holidays, one particular bit of Fujitsu kit would not come back up and required a tech from HQ in Japan to remote in and coax it back to life. A heroic weekend-long effort by IT team managed to get everything back on line by Monday.
A week or so later the IT team received an invoice from the UPS tech for his work. Suffice to say some colourful language and loud phone calls later the invoice was consigned to the rubbish bin, unpaid.