[Mashiro]

It's a very good idea to unplug as many devices as possible once power is out as @ikk157 has suggested. If possible it is also enough to configure devices not to power on after power loss (usually works with computers, servers, NAS systems or similar). However many home appliances don't have any configuration abilities to setup such things (fridges, TVs, etc...).

The reason why you should do this is actually simple to explain. During the startup phase of devices the power draw is a lot higher than during their usual operation cycle. This issue is known as "spikes" in the electrical system. The voltage and power draw sky rockets at the moment all devices start at the same time when power comes back. This makes the power grid unstable and can actually trigger another power loss if the switching components aren't able to serve the power demand needed during startup of all the devices.

So if you or your power company has old technology or bad components in the power grid... these spikes can actually just cause another outage. At worst some components might break like fuses and etc... thus once again delaying the time until power is back. I've seen even worse things happen though. It is very dangerous for example to power on all the switching equipment in a power plant because during the startup phase of the switching cabinets their power draw is so high... if something is wrong inside it can blow up the whole cabinet or kill people standing nearby if they don't have the necessary protective gear. Of course nothing that extreme can/will happen at home.

As an example you can always take the phase when you power on your car and start the engine. At the time you start the engine the power draw is insanely high. We're talking about several hundred Amps of power draw. However this is only necessary for a very short time (to start the engine). After that the power draw goes back to a more moderate and acceptable value. Automotive batteries are made to be able to serve this much power though. However if the engine is blocked or something else is broken and you keep trying to start the engine you will actually drain the battery because usually a running engine recharges the battery.

If the battery is too old or bad it won't be able to start the engine because it can't hold up with the power draw even for the very few seconds where it is needed to start the engine. Same can happen at home or at the company power grid just in huge dimensions as many people are connected to power company power grids.