Was curious enough to rig my Biolite to measure the internal power out from the TEG into the circuit board,
and simultaneously measuring the power consumption of the fan while the unit is fired up and all the while with a load connected to the USB port and sucking power out the the gadget at its continuous rated amount of 0.40amps @ 5volts.
Fan on Low speed uses 0.105amps @ 2.65volts while the TEG is generating 0.66amps @ 3.67volts.
So fan consumes 0.278watts. The USB port load is consuming 2.0watts and the TEG is generating 2.42watts
so that leaves an extra 0.142watts to run the computer and recharge the internal battery. Ok.
Fan on High speed uses 0.197amps @ 3.96volts while the TEG is generating 0.903amps @ 3.72volts.
Now the fan consumes 0.78watts. The USB port load is still being sucked at 2watts and now the TEG is
generating 3.36watts which leaves an excess of 0.579watts. So a device than is being recharged and consuming
more that 2watts is possible. The computer will manage the charge.
Anyway the catch is with the fan on high speed the stove burns up wood so incredibly fast its hard to keep up. Pause to eat or drink something and the solid wood you just crammed in will have magically turned to embers in seconds and the roaring flames you saw moments before will be gone and you'll need some thin sticks to get it flaming again.
Low fan speed gets the job done fine and is what I used exclusively when camping.