Battery Charger / Power Supply (Voltage, Amperage) Requirements for Phones, Laptops, Etc

When looking to buy a battery charger or power adapter for a device such as a phone or laptop, you may be unsure whether the one you buy will be sufficient or even blow up your device. Here are basic guidelines to keep in mind.

    The input voltage from the outlet to the charger should match or be very close. In the US, this is 110 volts. Unless you are buying a charger in a foreign country where the voltage is different, e.g. 220 V, this should not be a problem.
    Like the input voltage, the output voltage of your charger should match or be very close to that of the device you are plugging it in to. The input voltage requirements of a device can usually be found on the device itself. At the bottom of my Lenovo Yoga 910 laptop, it says “Input 20 V, 2.25 A”. Therefore, this particular device needs a charger that outputs 20 V.
    The output amps from the charger should be equal to or greater than the input amp requirements of the device you plug it in to. My Lenovo Yoga laptop has an amp input requirement of 2.25 A.

    • A charger with lower amps may charge a device but slower. Or, it may not charge it at all and the power supply may just turn off as it would not be able to adequately supply the load (laptop).
    • A charger with higher amps may charge a device faster than it would with a charger with amps equal to the value specified for the device. A device will not blow up if the chargers amp output exceeds the amp value specified for the device. The device will just accept however many amps it can handle.
    Power (wattage) is calculated as V (Voltage) x I (amperage). P = V*I. Therefore, for my Lenovo laptop, the minimum power requirements to power it is 20 V * 2.25 A = 45 W (watts). Therefore, it can take any charger that puts out 45 W or more as long as the output voltage is 20 V.
  • Input and output voltages should always match
  • Power supply amperage should be equal to or greater than the amps required by the load