I am using Samsung Galaxy S21. While charging my phone with a USB-C 65W Lenovo/Chicony power adapter with outputs supporting DC 5V/2.0A, 9V/2A, 15V/3A, and 20V/3.25A, how can I know exactly what power wattage is my device getting charged with? I tried using the Ampere app and the values range from 1000 mA to 2600 mA while the Voltage revolves around 4.1V?

Is there an app that can help provide power input details? Are there Android APIs to provide such information? Is it fine for me to keep using that charger? I understand Galaxy S21 supports USB C with power delivery, so it should be able to select the optimum voltage to charge my device?

From an article, I was expecting my charger to provide a 15W output but voltage x measured current using the Ampere app doesn't seem consistent with that number (5W?). What am I missing? How does USB Type C power delivery work in this case?

  • 1
    So in your opinion is the optimal voltage the maximum (to get the maximum charge)? You know that fast charging decreases the life time of the battery? The only reliable way to see what voltage and current is used is a hardware dongle that measures it on the cable.
    – Robert
    Jul 4, 2022 at 19:01
  • No, I don't expect fast charging. Probably, the use of optimal is not correct. I wanted to know how does the adapter and the device negotiate what voltage and amp rate to use? Wouldn't there be some logic? Jul 5, 2022 at 4:19
  • @MukulGupta yes their is a logic. But you won't find it because it's proprietary ;Market is flooded with at least 6 competing fast charge technologies. Do you expect them to reveal their secrets? //If your device is rooted, you have ways to control // See the charging algorithm (Source ) of an Anker power bank to get a sense of how complex it can be.
    – beeshyams
    Jul 5, 2022 at 5:37
  • USB PD is fairly complex //besides, it won't fit into "optimal" as asked in your question because legacy devices may be toasted, if optimal power is supplied
    – beeshyams
    Jul 5, 2022 at 5:53

2 Answers 2


If it's only to know the voltage and amp rate you are currently charging at for personal knowledge and not necessarily dependent on using software for calculation, I agree with Robert's comment about the dongle for I bought 1 about a year ago from an Oriley parts house around 8 bucks. Works flawlessly!


This needs a rooted phone in recent android versions. It works on all samsung phones i have used.

Using terminal emulator use this command:

while true; do cat /sys/class/power_supply/battery/current_now; sleep 9 ; done

Thes commands will print current every 9 seconds. Voltage is usually constant from chargers(not exactly sure) but as per my experience the higher the current the better the charger. This solution may nit work for you but i could work for other rooted users.

  • Hey, just adding that yes, voltage is constant from the charger. What can change is voltage between chargers. My new tablet eg can get up to 60W from a wall charger if the charger allows, and from the PD spec, you can see that for 60W it would be around 24V i guess, with 2.4A of current. Jun 11, 2023 at 21:25

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