How Did We End Up With Different AC Voltages?

(Last edited 5/14/2026)

Now that we’ve spent a lot of time talking all about capacitors, I want to shift gears for a minute before going back to the internals of a PSU and how they work and talk about the PSU’s job. 

Of course we all know that the PC’s power supply’s job is to convert the AC power coming from your wall to the DC power that all of your PC’s components need to function. Before we dive into how this is done, I want to talk a bit about the AC coming from your wall and why it’s different in different regions and how this impacts the different power cords that are available and how it may impact the PSU itself.

Let’s start with a bit of a history lesson.  It wasn’t too long ago when the world didn’t have electricity delivered to their house.  In September of 1882, Thomas Edison delivered 110V DC to homes in lower Manhattan, marking the first time electricity was centrally generated and distributed to multiple customers.  The reason 110V was chosen was because Edison’s light bulbs worked off of 100V and with the drop in voltage over the mile the DC power was delivered, using 110V would ensure the customer at the far end of delivery would receive 100V.

In 1881, British engineer John Dixon Gibbs and French inventor Lucien Gaulard (not Tesla) developed an AC transformer that was easy to produce and capable of managing high power levels. This transformer was showcased in London and later in Turin, Italy, in 1884, where it was subsequently incorporated into the city's lighting system. This transformer caught the eye of American entrepreneur George Westinghouse, who purchased the rights to utilize it in the United States.

 In 1885, American physicist William Stanley Jr. (still not Tesla) was recruited to create an electrical system that would rival Edison’s, based on the Gibbs-Gaulard design. By the following year, this design was implemented in a new power distribution system on the main street of Great Barrington, Massachusetts. It employed higher voltage over long distances, which could be reduced to lower voltages for indoor lighting applications.

In 1892, Edison General Electric combined with Thomson-Houston, Westinghouse's primary competitor for AC power, dropping “Edison” from the company name and creating “General Electric”. The board of directors, being from Thomson-Houston, entirely sidelined Edison, and the shift from Edison's initial DC delivery systems to AC started to progress. During this period, General Electric dominated three-quarters of the electrical industry in the U.S.  The irreversible change from DC to AC had begun.  But the voltage remained at 110V.

Around this time, two more things were happening in the world.  The electrification of Japan and the electrification of Europe.

Electrification of North America happened to coincide with Japan’s Meiji era, when they were rapidly modernizing by importing Western technology. Since Japan did not do a migration from DC to AC like North America, they did not feel the need to increase voltage by 10V to support 100V appliances, so they kept the voltage at 100V. In the late 1890’s, Kyoto was the first city to establish a public electric utility. With their generators coming from the United States, the power operated at 60 Hz.  Later, in the early 1910’s, Tokyo’s electrical grid was established, but Japan would obtain their generators from Germany and these generators operated at 50 Hz.  To this day, the West of Japan operates at 60 Hz while the East operates at 50 Hz.

Because Europe was electrified later than the Americas, circa 1890, with better insulation and transmission knowledge than what the Americans had to start with, they chose to use ~230V.  This higher voltage uses less current which reduces copper costs and improves long-distance efficiency. The use of ~230V spread to Asia, Africa, and Australia.

There are some exceptions outside of North America and Japan that do not use ~230V.  Taiwan is one such example. After World War II, Taiwan transitioned from Japanese colonial administration to the Republic of China government. During the reconstruction and expansion period, Taiwan’s power infrastructure was rebuilt and expanded rapidly, heavily influenced by U.S. engineering standards and equipment and aligned with North American practices, including ~110V distribution, 60 Hz frequency and NEMA Type A/B plugs. 

Brazil is another example of infrastructure influenced by U.S. engineering.  In the beginning, Brazil used 110V just like North America. But later, in the 80’s, they chose to increase their voltage to 127V.  The logic behind this is the slightly higher voltage would result in slightly better efficiency than 110V and still be compatible with 110V appliances. But Brazil does not only use “low line” voltage.  Parts of Brazil adopted 220V mains throughout the 20th century and now both voltages co-exist.