All my fish in reef tank died

Lots of things can go wrong. Here are some ideas:

• pH or ammonia spike : The larger the tank, the less likely spikes are, but all of my catastrophic failures like this were due to spikes

• Power outage : If the power went out, all electrical components would stop functioning, like the heater, filter, aerator etc.

• Feeder malfunction : Especially if you haven't tested it before, it could easily have malfunctioned, putting way too much feed or way too little.

• Domino effect : It's important to realize that decomposing fish bodies cause all sorts of issues and unhealthiness, so a single death could have caused a cascading effect

Addition to rib.usa's answer.

I think that typical fish could survive a week without eating.

Probably there was a power outage, which stopped all electric devices from operating. The time was long enough all the bacteria in the filter died and the filter became a source of poisonous substances. If the power was reconnected automatically by your utility, all these substances have been injected to the tank causing fish to die. Salt-water fish are much more susceptible to bad conditions than fresh water ones.

If there was "central AC broken", which I understand as there was a short-circuit in your tank. Perhaps the heater is down - maybe current flow killed the fish. I had such an event twice, however, all fish survived and did not even noticed.

What is also possible that there was a disease. Maybe some insect dropped to the tank and was eaten.

Unfortunately, if this was nothing with the equipment, you might never learn what had happened.