The Best USB Tester Is Already in Your Computer - Mac, Windows or Linux

Your Mac, PC, or Linux box already reports voltage, current, and the Power Delivery contract - no plastic dongle required. Here's where to find it.

If you’re searching for the “best USB tester” or a “USB-C power meter,” here’s the short version: you already own one. Whatever computer you’re reading this on - Mac, Windows, or Linux - is already measuring the voltage, current, and negotiated Power Delivery contract at its own USB-C port. The little plastic dongles on Amazon mostly repackage data your operating system reports for free.

Why a physical tester is the worse tool

Those $15-20 inline USB meters have three problems, on any platform:

  1. They read the wire, not the negotiation. A dongle sees volts and amps. It has no idea what contract the charger and computer agreed on, which profiles were offered, or why one was chosen. Your OS knows all of that.
  2. They’re a component in the path. Every meter is another set of contacts and a little resistance between charger and machine - so it can change the very thing it’s measuring, and on a laptop it often blocks the neighbouring port.
  3. They break. Tiny screens crack, connectors bend, and they burn out passing high wattage. Software lives on your disk for the life of the machine.

Where the data already lives, per platform

macOS exposes it through IOKit. IOPSCopyExternalPowerAdapterDetails returns the adapter’s identity, wattage, and its advertised PD profile menu, and the AppleSmartBattery registry reports real-time voltage, current, and power at the USB-C port. It’s the richest of the three.

Windows surfaces it through UCSI - the USB Type-C Connector System Interface - on modern hardware, which reports the active PD contract, plus USB device details through the standard device APIs. If your PC has a USB-C port and a recent chipset, the negotiation is readable.

Linux puts it in sysfs: /sys/class/typec/ exposes the USB-C partner and its PD capabilities, and /sys/class/power_supply/ reports the charging voltage and current. The whole USB device tree is under /sys/bus/usb/. Nothing to install to have the data - it’s already in the filesystem.

The catch: it’s raw

The data is there on every platform, but it’s buried in registries, WMI queries, and sysfs files that aren’t built for humans. That’s the actual gap a physical tester fills - not better data, just a screen.

Which is exactly what USB Connection Information does, on all three operating systems: it reads your OS’s own USB and Power Delivery data and shows it in your menu bar the moment you plug something in - the negotiated wattage, the full profile menu, the live draw, and the device details. The same numbers a dongle shows, plus everything a dongle can’t, from the port you already have.

We used it to measure every charger in the database - real wattage delivered, not marketing figures.