Transformer is a passive component where the input power is equal to the output power. This comes from the conservation of energy hence Pin = Pout.
Can we say the same thing for a DC-DC converter that Pout cannot be more than Pin? Let's say we have a boost converter and we only know its input current, input voltage and output voltage. If it is 5V to 12V converter with 100mA input current can we say that the theoretical max output current is (5V*100mA)/12V = 41mA?