If it is directly connected to the 12V output. Then it can be understood that the maximum input power of this module is 12*5A. As for the maximum output current of your DCDC module, it depends on the efficiency of your module and the internal current limiting design!! In addition, many multi-output switching power supplies, 5V or 3.3V, are actually separated on the 12V main output (internal DCDC chip), or directly from the transformer more than a winding, and then rectifier filter, this to consider the cost of the problem.