Because they’re not strictly 120 VAC, most electronics run on DC.
AC is AC - it doesn’t matter what the polarity is. There’s no way that reversing the polarity of an outlet could cause damage to a single-phase appliance. However it is still a serious safety issue, and should NEVER be done.
That is true for modern devices. The case is either connected to the protective ground or the device has to be double insulated, the latter being common for tools that only have a 2 prong plug but a metal case.
I would be worried about old devices that were made back in the days when 2 prong plugs were common. Lamps, kitchen mixers, even old vintage stereo equipment and all kinds of other things could end up with dangerous energized bits of exposed metal if plugged into an incorrectly wired outlet.
The danger is as mentioned, that some (older) devices may have the chassis or casing grounded to neutral. In Canada we mostly use 3-prong plugs ( a round ground pin below the typical N. American two-prong), especially for items that have a metal case, and the 3rd prong is ground.
Grounding a live current is not good. Electrocution and fires are common results.
A friend of mine had a house he rented out. After an electrical fire during renovations, the fire department came and turned off the main breaker. He then almost electrocuted himself on some wiring because the main power feed was connected in reverse, and the neutral was still live. That area of town was reknowned for the quality of workers who helped construct it.
Thank you. This is what I have been trying to say, errr, having been asking about.
I understand that, for many devices, the AC is rectified to DC. None-the-less, a receptacle that had been (incorrectly) wired w/ reverse polarity should not damage the device. As mentioned, the only potential danger is to a human.
And? Inverting the polarity on your AC isn’t going to invert the polarity of the DC that comes out of the power supply. Try plugging a wall wart power adapter in upside down and check the voltage that’s coming out of it with a meter.
gee…I dont know a damn thing about polarity—
but the Dope has definitely taught me about safety precautions for handling electricity:
Because I’ve read the classic how-to-change-a-broken-lightbulb thread.
(3 pages long, and funny… Honest.) 
And grounded in the basics.
Alright, enough with those - I have a short fuse.
It’s getting difficult to gauge the static to signal ratio in here. Some of the puns are real joules, but I think the short answer is I need to correct the reversed outlets when I get the time, but there’s no real rush.
You’ll have to pull the outlet out to tell if the wires are reversed. First, make sure the power is off to the outlet. If you don’t have a multimeter to check it with, plug a lamp into the outlet and keep turning off breakers until the lamp goes out. I have seen cases where the top and bottom outlet in a duplex outlet were fed from different sources, so it’s probably not a bad idea to plug the lamp into both the top and bottom outlets to make sure.
Once the power is off, unscrew the cover, unscrew the screws holding the outlet into place, and check to see if the black wires are connected to the brass screws and the white wires are connected to the silver colored screws. If they are backwards, reverse them. Make sure if there are two black wires that you move both to the other side of the outlet, and same with the white wires. Make sure you get the wires screwed on very tightly since a loose connection can get hot and burn your house down.
If the black wires are already connected to the brass screws and the white wires are already connected to the silver screws, then you have a worse problem. The wires are reversed somewhere upstream of the outlet. It would probably be best to have an electrician come out if this is the case, since there may be some very serious wiring issues going on with your house.
In any case, if you do not feel comfortable at all with electricity or have any doubts whatsoever, call an electrician and let them handle it.
That said, you may now return to the rather shocking puns in this thread. 
Can’t just use a circuit tester?
Lights for left and right slot AND lights for right slot and ground hole AND does NOT light for left slot and ground hole = Ok. Takes 10 seconds.
Of course, if the last guy ran the white wires as hot (you only know if you look) then there are gonna be other rats in the mill.
Let me clarify that by saying you’ll have to pull the outlet out to tell if the wires are reversed at the outlet, which is a simple fix, or if they are reversed somewhere upstream, which as you noted is a whole different can of worms.
Yes, a circuit tester will tell you if the wires are reversed in general. Sorry for the confusion.
that is with the ground hole down, which may be your case.
not everyone mounts receptacles like that. there are cases where people purposefully have the ground hole up.
Like outlets for lamps that are to be activated by light switches. Gawd I hate those things. I undo them whenever I get the chance.
The hole goes DOWN, light switches operate LIGHTS.
This is canon per the OCD code and is beyond…contestation.
Besides the stuff already mentioned, a major problem is the rest of the wiring.
How much can you trust that, if the guy doing the wiring was so incompetent as to make a basic mistake like this?
Much of the little I know of such matters was learned of necessity here in Thailand. The guy who wired our house did so many mistakes, I wonder if he was on drugs (or perhaps is one of these guys whose girlfriend ran off with a foreigner, so hates all foreigners :smack: ).
For example, neutral and phase are supposed to be distinguished by insulation color, but he used colors randomly. Also, wherever we had two lights and two switches, the left switch controlled the right light and vice versa.
The electricity-company people also have their foibles. Once, when repairing a transformer, they had our neighborhood miswired for a few minutes: two phases coming in, instead of phase and neutral. We lost a TV and a fan regulater that day.
The one key thing I’ve learned: When, e.g., replacing a lightbulb, it’s better to switch off the double-throw circuit breaker, rather than just the single-throw wall switch.
Question: posters speak of appliances where neutral and ground are connected. Are these not obsolete, since they’re incompatible with GFCI ?
Question 2:
Wasn’t the main breaker double throw? :dubious: 
True, but only if the ground (third prong) is properly connected.
Most lighting circuits are on a single pole, single throw breaker. In a miswired circuit the switch would break the neutral leaving the hot connected. The light would turn on and off just fine, but turning the switch off would leave the hot connected.
The main breaker will be double pole, single throw. I see references to double throw breakers on forums, but never saw one. Double pole means it switches 2 connections, often the 2 legs of a single phase circuit. Double throw means having a common that can be switched from normally open to normally closed. A 3 way light switch is an common example. They also come in center off for some applications.
And yes, devices with the neutral connected to the metal housing are oboselete except for 240 devices such as driers and stoves. There things still in service have 3 wires, hot, the other hot, and a wire serving as both ground and neutral. Thus the cabinet could be come hot if the neutral/ground was broken while it was turned on. New devices must now have 4 wire circuits. Our range is wired with SE, 2 hots with the neutral/ground wrapped around the outside.
There are still plenty of devices around with equal sized slots or blades put in service before polarized plugs came into use.