One of my stores had a power failure during a thunderstorm and I got called because the point-of-sale system was completely down. When I arrived, I found the UPS for the point-of-sale controller was turned off. According to the manager, when they called the help desk to report the power outage, the help[less] tech told them "I can't hear you. Turn off whatever is making that awful noise!"

From a newly remodeled store, I started getting calls every Monday morning that the printer at the receiving desk was out after a generator test. Sure enough, each time I'd go look, the printer was off and wouldn't power up. After about three weeks of this (and over $1,000 in printers!), I decided to be there when it happened. I got there about 10 minutes before the generator test usually started and set up my test equipment, connecting a DVM and an outlet tester and disconnecting the printer. The generator started, but as soon as it tried to take the load, it started stumbling and power to the entire store started bouncing. The DVM wouldn't stabilize enough to get a good reading and the outlet tester had all three lights flashing in various combinations. End result was I called the electricians to get on the generator and replaced several other pieces of store equipment. But I saved the printer!

Edit: spel