Why Some USB Ports Charge So Much Slower Than Others
USB charging is so commonplace that its taken for granted, but it’s a minor miracle that there’s finally a universal standard. Those old enough to remember what a headache it was to have a whole bin full of chargers, each of which belonged to a different gadget, can attest that things are much better now that most things are compatible with USB charging.Even so, there is a wide range of different USB standards, and charging speeds can fluctuate wildly between them.
If you’ve ever wondered why a charging brick can juice up your phone so much faster than the USB port in your wall outlet, or why different ports on the same computer sometimes charge at different speeds, the answer is that it depends. Sometimes, it’s a limitation of the physical hardware or USB specification, while in othre cases a manufacturer may implement faster or slower charging speeds on a per-product basis. Older USB standards can still be found in many devices, and they simply aren’t capable of delivering the same power as newer ones.
Other variables aside, a few different things can determine the top charging speed of a given USB port.Those are the USB generation, Power Delivery (PD) generation, and limitations or customizations set by a device manufacturer. The limit at which a USB port can send or receive a charge is 240 W via USB4 Version 2.0, as of this writing. Most devices don’t hit this threshold, though some new laptops are showing up on the market that do charge at 240 W over USB-C. Conversely, USB can charge as slowly as 2.5 W. Those sluglike speeds are most commonly found in USB 2.0 ports – increasingly rare on newer hardware but still quiet common in places where old ports were installed years ago, such as public charging ports at airports and coffee shops, USB wall chargers in outlets around your home,or car dashboards.
The USB Power Delivery (USB-PD) standard also plays a role. It negotiates a handshake between a charging port and the device being charged to avoid any damage. PD 2.0 was capable of up to 100 W charging,while PD 3.1 is capable of the 240 W charging speeds we just discussed while using USB4 Version 2.0. There are also proprietary power negotiation technologies such as Qualcomm Speedy Charge and Oppo SuperVOOC, which might potentially be used in certain phones and other devices.
Lastly, a device manufacturer may impose custom limits on USB charging at the level of the host controller on the motherboard. Usually,those limits are meant to protect the device. As an example, a port might have hardware that’s technically capable of 240 W charging, but if it drew that much power from it, it would fry the system.
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