I'm working on an project which will be given to some friends and will be open-source too.
I need to choose the power supply connector (5V or 12V @ 3A) and I'm thinking to barrel connectors. I found there're 2 version of them, the 2.1mm and 2.5mm for the internal pin.
I read also the 2.5mm male will fit the 2.1 female but connection is not stable, so it is not a reliable solution to choose the smaller one to accept both.
So, which is the most used? The goal is to have the maximum compatibility with existing PSU around the house.
Best Answer
Alas, this is difficult to pin down. "Most used" depends on your industry, your region of the world and the year you ask the question.
For a long time every manufacturer would pick their own and supply the plug to suit. Consumers who tried to connect their own would quickly discover they'd fried the appliance by connecting the wrong voltage to it. So people learnt to limit the mixing and matching of supplies and devices, and manufacturers were motivated to pick uncommon sizes to prevent misconnection.
It's probably only since the Arduino that there's been much interest in supplying your own supply, and the question of compatibility became of general concern. The Arduino happens to use the 2.1mm barrel jack, and the Beaglebone followed suit.
So 2.1mm has become a de-facto standard in the maker community, which has influenced a lot of electronics. But this is neither official nor stable, so I'm afraid your goal of "maximum compatibility with existing PSU around the house" is probably largely unachievable in April of 2019.