Adjustable USB Power Supply

Close up photo of the USB power supply

Update 09/03/21: I’ve put a few of these devices up for sale on eBay to fund my projects if you’re interested in one.

Update 05/03/21: I’ve added some information about the accuracy of the power supply.

Update 03/03/21: I’ve retaken the photos on this post as I got the white balance on my camera badly wrong and everything came out with a green tint.


When I was at university one of the more useful tools I had when working with electronics was an adjustable benchtop power supply. With it I could quickly set a voltage or current and power anything I wanted. This was quite handy when I just wanted to check if something would turn on. Now that I’m getting back into electronics as a hobby I can’t yet justify (or afford) a benchtop power supply so I’ve been looking around for some cheaper alternatives and think I’ve come across just the thing.

A small box of tricks

Photo showing the USB power supply

This little device is no larger than a box of matches, is powered by USB, has a display, a pair of quick-release terminals, an adjustable output voltage between 1-30V and an adjustable output current between 0-2A but more on this later.

I’ve been using several of them for a couple of weeks now and I’m impressed with what they can do for the money. They’ve powered LEDs, PIR sensors, development boards and video pattern test generators amongst other things.

They don’t produce anything near the power you get from a benchtop power supply, it tops out at 15W, but if you’re mostly working with low power circuits then this is more than enough.

Using the power supply

There are three ways to power the device. You can plug it into a USB-A port on your laptop/hub or there’s a USB-C and a micro-B USB socket so it will work with your mobile phone charger and cable.

Photo showing the USB inputs on the power supply

For the output there is a USB-A socket and a pair of quick-release terminals that are electrically connected together (i.e. they don’t work independently).

Photo showing the USB power supply connected to a charger

The device powers up automatically when you connect it to a charger. Depending on how the device has been configured when it left the factory the output may come on automatically however you can change that if you press and hold the on/off button. There’s a handy LED that lets you know when the output is on.

Photo showing the on/off button of the USB power supply

Using the dial allows you to change the measurements displayed on the top and bottom half of the screen. It can show you the input and output voltages(V), the device temperature(°C) – which is useful to know when drawing higher currents, the output current(A), power(W), capacity(Ah) and time(s) – the last two are measured only when the output is on.

Photo showing the control dial and quick-release terminals

Pressing and holding the dial allows you to set both the output voltage and current. If you set a limit on the current the device will supply it up to that point after which it will not allow the current to go any higher and a light will illuminate. The power supply calls this constant current mode but it’s not really which initially confused me when I was trying to power an LED connected directly to the quick-release terminals.

Photo showing the USB power supply powering an LED

Drawing more power

According to the documentation for this device trying to supply 15W using a 5V USB charger will mean you draw over 4A of current when you consider efficiency losses (i.e. cable resistance, voltage conversion losses etc.). Most 5V USB chargers aren’t capable of this so it also supports a variety of fast charging protocols. These essentially increase the input voltage to allow more power to be delivered without increasing the current. The fast charge protocols below are supported.

Quick Charge 2.0 (Qualcomm)
Quick Charge 3.0 (Qualcomm)
Adaptive Fast Charge (Samsung)
Fast Charge Protocol (Huawei)
Super Charge Protocol (Huawei)

Using one of these fast chargers you are able to achieve the 15W maximum output from the power supply. It doesn’t automatically detect if a fast charger is being used you need to enable it. There is an auto mode that tries to detect which protocol is available from the charger but it takes time to run and isn’t always successful so I don’t use it. Again handily there is a light that illuminates when fast charging is being used.


Photo of the USB power supply connected to a multimeter

I connected the power supply up to my cheap multimeter and measured the output voltage at 5V intervals.

Voltage SettingMultimeter Reading

At voltages above 20V I had to switch to a different range on the multimeter so lost a bit of resolution however the power supply remained accurate accross its entire output range. Just a note to bear in mind but this was done without any load on the output.

Wrapping up

Overall for under £15 this is a very capable device that does everything I need for my small projects and I would highly recommend it if you’re in the market for a low-cost power supply – you can find it on eBay if you search for ‘ZK-DP3D’.