I performed some extra tests with my USB fridge (see Quickpost: Testing A USB Fridge).

Here is how the temperature evolved when I put a can with cold water (around 12° C) in the USB fridge:

The temperature increased around 2° C over a period of 12 hours (room temperature was around 17 °C).

That required around 57 Wh.

And the temperature at the top of the can increased more than at the bottom:

For reference, here is how the temperature evolves of a cooled can of water left on the desk in that same room (so not inside the USB fridge):

Quickpost info