If your project board doesn't have a DC jack and you want to connect DC power adapter from the wall, you can use this adapter. It has 5.5mm x 2.1mm female jack on one end with center positive connection (the most common).

On the other end, there is a screw terminal block where you can insert your wires in. The polarity of the terminals are embossed, positve (+) and negative (-), so that there is no guessing work needed there.

We find that this adapter is handy when working on our LED project.