Power Supplies Adapters Connectors Barrel Power

Introduction

If you've been tinkering with electronics long enough, you've probably accumulated a collection of devices that arrived without a power supply or have been separated from the original power supply. Maybe it's a surplus-sale monitor, used router, mini-PC, audio amplifier, security camera, or other hardware you rescued to “do something interesting with it someday."

The problem is usually not determining the required voltage or polarity since a quick look at the label on the device, or an online search, often reveals that information. The real challenge is figuring out what barrel connector size the manufacturer used.

That's where the 28 PCS Universal 5.5×2.1mm DC Adapter Kit from DFRobot comes in. The kit provides a collection of barrel connector adapters that convert a standard 5.5 × 2.1 mm DC plug into a wide variety of other connector formats commonly found on electronic devices. DFRobot positions the kit as a power interface conversion solution for electronics maintenance, prototyping, repair, and testing applications. This simple kit turns out to be an excellent tool for identifying unknown DC barrel connector sizes.

Most of us already have access to a bench power supply, adjustable DC supply, or a collection of DC adapters with a 5.5 × 2.1 mm barrel connector, but the device you're trying to power rarely uses that exact connector. Instead of purchasing multiple power supplies simply to test a device or fumbling with a caliper trying to measure small diameters in tight spaces, this kit lets you quickly adapt a known-good power source to a variety of connector sizes. DFRobot describes the kit as supporting numerous DC connector formats commonly found on laptops, displays, audio systems, and other electronic equipment.

The process goes something like this:

1. Verify the device's required voltage.
2. Connect a suitable power source with a 5.5 x 2.1 terminal adapter, ensuring correct polarity.
3. Try adapters from the DFRobot kit until one fits the device.
4. Confirm the device powers up.
5. Identify the connector size.
6. Purchase a permanent power supply that uses the correct connector.

This process can save a lot of frustration when dealing with unknown or second-hand hardware.

An Important Note About Safety

Before we go any further, it's important to understand what this kit does not do.

The adapters only change the connector geometry.

They do not change:

• Voltage
• Current capability
• Polarity

DFRobot specifically notes that the kit does not perform voltage conversion and that users must verify the power supply requirements of the connected equipment before use. Applying an incorrect voltage can damage the device. Always remember that just because an adapter fits does not mean the connected power supply is appropriate.

The Identification Problem

Suppose you've found an adapter that fits your device perfectly. Great, now what size is it?

DFRobot has a numbered diagram showing all of the adapters, listing each connector's dimensions/style. However, the connectors themselves are not labeled with these numbers. Several connectors look extremely similar, and they share only a few different colors. You may think you can just measure whichever fits your device with a caliper, but because some internal diameters differ by only a few tenths of a millimeter, measuring them accurately can be challenging and time-consuming.

Luckily, I found that each connector has a small letter molded into the body of the connector, so to solve this problem, I went through the entire kit, matched each numbered adapter to its molded identification letter and tip color, measured and documented each connector size, and created the following reference table.

How to Use This Table

After finding an adapter that fits your device:

1. Locate the molded identification letter on the adapter body.
2. Note the color of the tip insert.
3. Use the table below to determine the connector size.
4. Verify the connector matches the image using the red reference number in the manufacturer's diagram.

Compiled from hands-on identification and measurement of the adapters contained in the kit.

Why the Label and Color Matter

You might wonder why the table includes both the molded letter and the color.

The reason is that neither identifier is unique on its own.

Several adapters share the same letter, including:

• H
• C
• D
• I

Likewise, multiple adapters use the same tip colors, particularly black and yellow.

Using the combination of:

• Adapter Number
• Molded Letter
• Tip Color

provides a reliable way to identify the correct connector size without needing to break out a set of calipers every time.

A Real-World Example

Recently I acquired a used display that requires an external power supply. The label indicated it needed 19.5V DC, but the original supply was missing. I connected a current-limited 19.5V bench supply equipped with a 5.5 × 2.1 mm barrel connector, ensuring correct polarity, and began testing adapters. After trying several options, I found an adapter that fit perfectly.

Looking at the adapter, I saw it had the letter “A” molded into the body. Looking at the table, I see there is only one adapter with the letter A, so that means this adapter is:

• Number 19
• Size: 6.0 × 4.4 mm with center needle

A quick look at the image provided by DFRobot matched the appearance, verifying that these were the right specifications for this connector.

Now I knew exactly what connector to look for when looking for a replacement power supply, whereas without the reference table, I'd know this adapter fits, but I still wouldn't necessarily know what connector size to search for.

Final Thoughts

At first glance, this appears to be a simple adapter kit, and it is, but its greatest value isn't necessarily powering devices permanently. It's helping identify unknown connectors quickly and safely during troubleshooting and testing!

For those of us who frequently work with second-hand electronics, surplus hardware, repair projects, or home lab equipment, being able to determine the correct barrel connector size before purchasing a replacement power supply saves both time and money, and this adapter kit makes that process easy.

So, with this kit, the next time you find yourself staring at a device with a missing power supply and wondering, "What connector does this thing use?" you'll have a much better place to start.

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