For some CPU fans 5 V will make it run but not at full speed. I didn't want to sacrifice any of my chargers so I actually bought a DC adapter with selectable voltage from Walmart. It was less than $20 so not too bad, and it lets me select from 3V to 12 V (a few discreet settings - not continuous) which is nice because on cool days I run it at 7.5 V to keep the things really quiet, but on warmer days I can crank it up to the full 12 V