How many volts is a USB port?
A USB port can give 500 mA output max provides 5 Volts x 0.5 Amo = 2.5 Watts. With real world efficency losses (nominally 80~90% efficent), you can provide a Higher Voltage with Less Current, or a Lower Voltage with More Current, but you can't create powerout of nowhere.
You could use a Lightning connector plugged into a computer (via USB), an iPhone charger connected to a wall socket, or an iPad charger connected to a wall socket. A PC USB charger delivers 2.5 Watts of power (5 volts at 500 mA). An iPhone charger delivers 5 Watts (5 volts at 1000 mA).
- For example, 4.5 volts is 1.5 volts (AA primary battery) 3 times and 36 volts is 3.6 volts (Li-Ion battery) 10 times. Now there're laptops that use external power supplies rated at exactly 19 volts.
- It is simply a USB cable, which allows my tablet to charge from a DC USB port in a car or laptop. Both sides have DC, so no conversion is required. Now, here is my tablet's AC charging solution. The same USB cable plugs in to a little black box that plugs in to an AC outlet – the box converts AC to DC.
- Apple gives you the 2.1 Amp 10 Watt charger so it won't take a day to charge your iPad due to the battery being much bigger. Most USB Hubs produce the .5 Amps even though they have an external power supply you plug into the wall.
For mobile phones and other mobile devices like the Kindle that charge with USB, the voltage is typically 5V. A laptop charger might be as high as 20V or 25V. You can usually find the voltage your device needs on the device itself, on the battery, or if all else fails, on the manufacturer's web site.
- All USB cords carry the same 5V, regardless of if it's got a 30-pin head or a microUSB plug, whether it's first-party or third. That means DC chargers are now brand agnostic; if the volts, amps, and connectors are compatible, an Apple wall wart can charge an HTC just as easily as a Samsung.
- In the USB 1.0 and 2.0 specs, a standard downstream port is capable of delivering up to 500mA (0.5A); with USB 3.0, it moves up to 900mA (0.9A). The charging downstream and dedicated charging ports provide up to 1,500mA (1.5A). It also supports power draw of 1.5A and 3A over the 5V bus.
- A power adapter that generates the 5 volt DC standard required by USB. The charger plugs into an AC outlet, and a USB cable plugs into the charger. USB ports on computers have an upper limit of 500 milliamps; however, USB chargers that come with cellphones and other devices handle one or more amps.
Updated: 2nd October 2019