How to Measure USB-C Power with a Voltage & Amperage Meter
By Plugable #1 in Docking Stations and USB Devices ~ Plugable ... | Published: 2026-10-24
Category: How-to Guides
Learn to use a USB-C voltage and amperage meter to test charger output, check power delivery, and troubleshoot charging issues with step-by-step instructions.
Quick answer
Plug a USB-C voltage and amperage meter between your charger and device to read real-time voltage, amperage, and power delivery—including 240W EPR—and identify underpowered chargers or faulty cables.
Why use a dedicated USB-C meter instead of a multimeter
A standard multimeter requires breaking the cable and probing live wires, which is risky with USB-C’s high-speed data and power lines. A USB-C inline meter like the Plugable USB-C Voltage & Amperage Meter simply plugs between the charger and device, showing voltage, amperage, and power direction without any wiring. It also passes through USB data, so you can test while the device is actively communicating.
What to look for when testing 240W EPR chargers
EPR (Extended Power Range) chargers can deliver up to 240W at 48V. Not all USB-C meters support this higher voltage. The Plugable USB-C Voltage & Amperage Meter is rated for 240W EPR, so it can safely measure the full output of modern high-power chargers. If your meter isn’t EPR-rated, it may cap readings at 100W or even get damaged.
How to measure USB-C power in 4 steps
- 1. Connect the meter between charger and device: Plug the USB-C meter into your charger’s output port, then connect your device (phone, laptop, or power bank) to the meter’s other USB-C port. The meter powers on automatically and shows the current voltage and amperage. Make sure the meter is oriented correctly—some meters have an input/output direction; the Plugable model is bidirectional.
- 2. Read the real-time display: The meter screen shows voltage (V), amperage (A), and calculated power (W). For USB-C Power Delivery, voltage may start at 5V and step up to 9V, 15V, 20V, or higher for EPR chargers. Watch the numbers stabilize after a few seconds. If the voltage stays at 5V when you expect fast charging, the device may not be negotiating PD properly.
- 3. Test under load: Use your device normally—charge a laptop, transfer data, or run a power-hungry app. The meter updates in real time. Compare the reading to your charger’s rated output (e.g., 60W or 240W). A significant gap may indicate a weak charger or a cable that can’t handle the current. A voltage drop of more than 0.5V under load often means the cable is too thin or too long for the power level.
- 4. Check power direction and data passthrough: The Plugable meter shows an arrow indicating whether power flows from charger to device or vice versa. It also passes USB 2.0 data, so you can test charging while transferring files or using a keyboard. This helps confirm the cable supports both power and data simultaneously. If the arrow points away from the charger when you expect charging, the cable may be wired for data only or the charger isn’t negotiating PD.
Product used in this guide
- Plugable USB-C Voltage & Amperage Meter for High Power Devices (240W EPR): The Plugable USB-C Voltage & Amperage Meter fits in a USB flash drive size, supports 240W EPR, and shows real-time voltage, amperage, and power direction while passing through USB data. You can test any USB-C charger up to 240W without extra wiring, and still use the device normally during the test.
Plugable USB-C Voltage & Amperage Meter for High Power Devices (240W EPR)
