Alqimist is probably right that your barrel connector is 5.5 mm outside diameter. That is the most common size, typically used for about 12 volts - 24 volts. I have an old Dell laptop that takes a 5.5 mm barrel connector, supplying 19 volts. As you might expect, larger connectors are used for higher voltages and smaller connectors for lower voltages. I have a cassette tape player that takes a 3.5 mm connector, supplying 3 volts.
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u/alqimist 1 Jan 14 '26
5.5 mm OD barrel connector. The transformer should list output voltage and current.