> To not waste the 24W on the 12V I will probably use the DC/DC converter in the pictures and go from 12V to 5V for efficiency reasons...
The more common converters "burn" the voltage difference times ampere. So 14W will be emitted as heat by the converter, a matching heatsink would be somewhat important.
Instead of 24W wasted it is now 14W wasted. I am not sure if this is worth the effort.
Linear regulators went the way of the Dodo long ago for applications like this. HF DC-DC converters are the way to go, at the currents involved here you'd be paying more for the heatsink in a linear setup than for the whole DC-DC converter.
These things you are talking about are usually called _voltage regulators_. DC/DC converter usually refers to the switching converter, they are very efficient.
The more common converters "burn" the voltage difference times ampere. So 14W will be emitted as heat by the converter, a matching heatsink would be somewhat important.
Instead of 24W wasted it is now 14W wasted. I am not sure if this is worth the effort.