The DC/DC converter is integrated into the Delta-Q QuiQ-dci charger. That is what the -dci means.
This solves the problem of how to power the 12V systems without the original 12V battery and a separate charging system. There are other ways of solving this problem, but most agree that a DC/DC converter is the most elegant solution.
Other popular choices for motorcycle DC/DC converters include Vicor and Surepower models. It is advantageous to get one with both switched and unswitched output. This allows you to enable the switched output through your original key switch, thus turning on the 12V systems. A second switch, such as the run/kill switch, can then be used to turn on and turn off the drive system through the contactor, either directly (if the contactor has a 12V coil) or through a smaller relay.
QuiQ-dci DC/DC Converter Output
A good quality DC/DC converter will feature an extremely low power draw, probably less than 1W, to maintain the unswitched output under no load. And it will have an isolated output, meaning the high voltage side and the 12V side do not share a common ground. This is an important safety feature if your 12V system is grounded to the frame.