Power is power, except when it isn't. The general socket power available across the world varies from country to country and even within some countries. There are a multitude or reasons for why this happened but our main concern now is how to deal with it so that our systems can run effectively regardless of where we ship them.
In total there are about 16 different voltage and frequency combinations around the world. These variations are generally lumped into high and low voltage groups. Low voltage is about 85 to 130VAC and high voltage is 170 to 264VAC. Frequencies are either 50 or 60Hz except for unique situations on aircraft or ships where you can find 400Hz. At one point, early in the history of electric generation, there were 10 different frequencies in use just in London but as technology matured most systems gravitated to 50Hz or 60Hz. Higher frequency power has been used on airplanes and ships since it allows for all magnetic components to be smaller meaning lighter motors and generators, the downside to high frequency is that is does not handle long distances well but in closed environments this is not as much of an issue.
When it comes to plugs to get to that power you have 14 types that are recognized by the International Electrotechnical Commission and that doesn’t include the unique ones for 240V in the USA or three phase connections. There are even more when you look to the National Electrical Manufacturer’s Association which adds about 16 plug/receptacle variations to North America based on voltage and current rating.
In the United States the standard plug voltage is 120V at 60Hz and the plugs are NEMA 1-15A which is the ungrounded double blade or the NEMA 5-15A which is the grounded variant. If needed sockets can be wired up to serve 240V like on a clothes dryer or three phase wiring is available in main industrial settings for the very high power machines. There are other plug styles to prevent you from accidentally plugging into 240V or plugging a 20A device into a 15A socket and popping a breaker.
In most of Europe the plug voltage is 230V at 50Hz but the plug situation is all over the place with potentially 9 different plugs of which some are compatible with one another and others are not. This variation among plugs means that power cable selection in Europe is quite important when shipping finished systems.
A unique case of multiple voltages is Japan. In the east you have 100V at 50Hz which was started by the Tokyo Electric Light Company and used German made power equipment. In the west you have 100V at 60Hz which was started by the Osaka Electric Lamp Company and used equipment built by General Electric to the US power standard. This presented a significant issue after the Japanese Tsunami in 2011 which knocked out a lot of generation capacity in the north and there were not enough frequency converters to utilize energy from the 50Hz grid resulting in power rationing in the affected areas.
To bridge this issue some power supplies have switches to move between the low and high power groups. When you flip to the lower voltage input a voltage doubler is added to the circuit. This approach is most useful when you need to support the full range of AC inputs but need to do it cheaply. Recently most voltage doubler circuits have been designed out in favor of active Power Factor Correction, new efficiency standards in many countries make active PFC necessary once you pass a certain power threshold.
A big benefit of active PFC is that you get universal AC input without needing customers to flip a switch or be concerned about which voltage they will get in which country. Universal is considered to be about 85-240V or 264V AC (50/60Hz), heck there are even designs that can do ultra wide ranges like 85 to 528VAC but at very low power like this reference design from TI based on the UCC28722. Lower power power supplies, say below 75W, can many times achieve universal input using an intelligent Flyback design. By providing a universal input capable power supply you simplify the user experience and reduce the chances of someone damaging a system by not configuring it properly for the country they are in.
Even with all these different standards you can many times design to a universal input and utilize an IEC320 C14 input. There are power cables from most country specific plug to the C13 mating connector saving you from having to try and meet every plug standard