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Search for USB power monitors and you will come across hundreds from a variety of sellers. While I have and regularly use a number, the one I keep coming back to is the PortaPow Power Monitor V3.
I've been using PortaPow hardware for well over a decade. Based in London, UK, the company was founded in 2005, and, according to its website, started out "pioneering the use of power banks to keep mp3 players singing long past the original battery life." Regular readers might remember the name because the company also makes USB data-blocking condoms, which are unfortunately a must-have item these days if you use untrusted USB ports for charging your gadgets.
The PortaPow Power Monitor V3 combines a USB power meter and a data blocker into a single, convenient, low-cost, reliable tool.
Must read: Best of the best gadgets of 2020
Basically, the Power Monitor V3 is a little black box featuring an LCD, two USB-A ports, one USB-C port, a button, and a USB-A connector on a short pigtail cable. You plug the pigtail into a port, connect a load to one of the built-in ports, and the LCD shows you the power consumption.
One of the USB-A ports blocks data while the other does not, while the single USB-C port also blocks data.
It can handle voltages between 3 and 12 volts, and loads between 0.01A and 4A.
The button allows you to switch between nine memory slots, which is really handy when you are testing.
It works great.
The Power Monitor V3 is an updated version of the Power Monitor V2, which was discontinued in August 2020. The older version did not feature a USB-C port. I put years of use on the V2 and it's still going strong.
I use my PortaPow with USB loads (like this or this) to test charger and power bank output, and also to measure the capacity and discharge capabilities of power banks. It's also handy for testing the output of portable solar panels designed for charging power banks and portable power stations.
A quick note about USB loadsThe fanless resistive loads can become very hot. Hot enough to do damage, such as burn skin and melt cutting mats and such (been there, done that). Take care!
The PortaPow Power Monitor V3 is currently available on Amazon for $12 (the listing shows the old version, but the product shipped is the new one).
I highly recommend you get one for your toolbox.