The cleaning lady probably pulled the plug on the server to plug in her vacuum
You laugh, I have seen this exact situaiton or where the vacuum was plugged into the same circuit as critical comms and tripped the breaker.
The absolute best one was where the 4 story office foyer outlets were on the same circuit breaker as the buildings critical telco circuits from the local Bell provider. There was a 24 hour Ops Center in the building, the painters had an electric man lift they plugged into the foyer outlet to change light bulbs and/or paint, the cord was damaged, tripped the breaker. Comms ran off the Bell provider battery bank for a few hours until 3 am when all outside connections, telco and data connections died. Ops Center staff did not have a key for the main Telco closet or separate electrical closet where the breaker panel was. Somehow the local Bell provider had access to the phone closet and luckily he was driving a bucket truck with a generator.
He fired up the generator and ran an extension cord into power all the telco gear and get the Ops Center back online until the building maintenance guy was kicked out of bed and had to drive an hour to the facility!
As far a cleaning and vacuum, the last few Ops Centers I had input into when building had central vacs installed. Quick, quieter and on its own dedicated circuit not tied into critical power.
I have seen it all at one point or another, the good, bad and the ugly.
Anyway, hopefully in the future someone can update folks of planned works and outages as a matter of courtesy?