In any power supply, the power input will always be larger than the power output. The extra power becomes heat in the power supply.
Any power supply will have rated input voltage, and it will take whatever power from the supply that it needs. You can't force it to take more power than it needs just by connecting it up with bigger cable.
The mains sockets in your house can run big heaters that are up to 3 kW on 230 V ac supplies or about 1.5 kW on 120 V supplies, but it is fine to plug a cellphone charger that is rated at 5 - 10 W into the sockets, and it will only take a few mA from the mains.
The inductor in a SMPS has a maximum current. It is usual for the control circuit to limit the current to a bit less than the maximum.
The capacitors on SMPSs are large enough that the input current has to turn on and off many times to get the output voltage up from zero to the rated output. So when the output voltage gets up to the rated voltage, the input current will turn off, and the energy stored in the inductor will end up in the output capacitor. That will only be a very small voltage rise over the rated voltage. The voltage control circuit will then not turn the input current on again until the output voltage has fallen to less than the rated voltage.