I am in the process of building a DSLR cooler (I use it for astrophotography) using a couple of TEC1-12703s (12V 3.3A) or TEC1-12704s (12V 4A). The ultimate idea is to run the TEC's at a higher power when initially cooling to the target temperature, then throttle them back to maintain the temperature as best as possible.
The bulk of the cooler will use an Arduino (~15mA), a power-on LED (~20mA), a couple of sensors (~1-1.5mA each when measuring, ~40µA standby), and a couple of fans (~65mA). So total power draw from most of the parts won't be very high (<200mA).
A couple of the PWM outputs on the Arduino will be used to switch IRBL8748PbF N-channel MOSFETs to deliver power to the TECs. The TEC power will be LC filtered, and a schottky diode will be used on each filter to make sure I don't fry the FETs (not sure if that would really be a problem, but I threw them in just to make sure I don't have weird voltage spikes at the FET drains). Ultimately the fan speed would also be controlled with PWM outputs the same way as the TECs are, with a MOSFET, however to start they will just be connected to the main 12V source and run at full power.
With two TECs, that is potentially up to 8.2A of total current. Even with the lower power TECs, that is still 6.8A of total current. I am beginning to wonder if I can send that much power through a standard 5.5mmx2.1mm power jack. I am also beginning to wonder if I can find a DC power switch that could handle over 8A.
If finding a switch that could handle that kind of power is unlikely, might it be possible to power the TECs directly off the power from the jack, and put the switch after that power line? Since the TECs won't actually power up until the MOSFETs are switched on, they should remain off until the power switch is flipped. At that point, only a few hundred mA would be pulled through the switch. Which would leave only the power jack in question.