These small no name DC-DC step-up/down converter PCBs are ideal for small projects of up to (nominally) 600mA. Mine are called "DC-DC Automatic Buck-boost Modul 2.5V-15V to 3.3V 4.2V 5V 9V 12V Output" on ebay. Watch out, there is a newer, very similar looking version of this board with five instead of four connectors pins, they won't fit this case. With the help of four 3-pin male headers and a bit of soldering, the case can be used with the fischertechnik 2,6mm plugs or female dupont connectors.