Hi Bryan,
These little transformerless modules that supply low
voltages at low currents usually use a capacitor as a
'dropper' at least thats my experience.
It has to be AC working of course, and simply wired in
series with a small load.
It has to be mentioned that a fuse for the load is in my
opinion very necessary, because a dirty pin or any poor
connection can cause vastly excess current to flow in
the load.
For a small fan such as you describe, i would suggest
a capacitor of 2 or 3 mfd, i am guessing that your
main supply is 110v it seems more common than mine at
240v.
The load would be a small resistor of about 200 ohms
and a diode bridge to give you the DC.
Across the diode bridge put a 12 volt zener and a small
electrolytic, maybe 30 MFDs or so.
The zener has to be about 2 or 3 watts, and with no
load on the supply it may run barely warm.
I have made many such supplies.
Best of luck with it,
John