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Most electronic devices use 3.3V, 5V (all USB devices), 9V or 12V (very often for electronic music gear), and we usually all have dozains of such wall adapters at home. Even desktop computers have usually 5V and 12V power supply (ATX power supply).

Is there a historic reason (or electronic reason) why laptop computers are usually around 20V?

Why don't they use a quite standard 12V?

Linked question: Why is a laptop power supply output voltage different from its battery? but here a bit different, I'm not looking for the reason about the voltage being different from the laptop's battery, but rather why it's different to the standard 5V / 12V used in desktop computers.

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  • \$\begingroup\$ Possibly because the laptop batteries are restricted in terms of soace so a higher voltage means fewer bulky cells... \$\endgroup\$ – Solar Mike Aug 23 '19 at 15:39
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Two reasons. First, often the cell stack is already close to or well above 12V so internally the laptop would have to step up the 12V charge. Pack voltages of 11.1 and 14.4V are common. Charging these voltages is easier to manage with a step-down type regulator vs. a step-up or buck-boost.

As a couple of examples, a Li-ion 11.1V (3s) battery will have a topping-charge voltage of 3*4.2=12.6V. A 14.4V (4s) battery pack will be 16.8V.

Second, going in with higher voltage allows the charge cord and PSU to be more compact as the required currents are lower.

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