Huh? Home computer fans are 99.97% of the time DC.

For years, I've used a "wall wart" type supply to run a computer fan for various needs; just make sure the amps that it can supply are equal to, or greater than the amps that the fan will draw.

FYI... I have a bin full of "wall warts" to choose from - when I get rid of old gear, I always keep the power warts so I will always have a handy supply. Solder on a different end, if needed, heat shrink tubing to finish the job right.