We all use breadboards for prototyping. We all use DC Adapters to add power to them. But i used to do this by simply taping the wires to the DC Jack and then use it on the breadboard. This was always loose and clumsy and i always has to find out the polarity as some manufacturers are smart to not ground the outer shell. I even blew an IC this way once, when it was taken for granted. Some manufacturers do keep the outer part (shell) as positive while ‘most’ keep it negative!
So, I found out a better way to make breadboards compatible with DC jacks and polarity issues. This is small board with headers that plug into the breadboard. It has a diode to make sure nothing flows reverse and a small 0.1uF cap to provide some rudimentary decoupling.
I quickly designed the board,etched it and filed it to shape.