Breadboard power supply hits both rails

Now this is a good idea.  It allows you to take a DC power supply (batteries, or plugged into the wall - a "wall wart") and it puts either 5V or 3.3V DC onto both the rails on a standard breadboard.  For those cases when you're throwing something together, but don't have a more elegant power source.

Of course, if it's using a controller, you could also just use an Arduino Nano.