99% of case fans are 12V. any house hold D/C adaptor that puts out 12v would work. there amperage is so dead low usually its not close to being an issue. most common fans range from .06-.05 Amps (60-70 milliamps) and use about .8w

Im a PC Tech, i jerry right computer fans for everything. its simple.

an easy equation for current (amperage) conversion to watts or voltage if you ever find your self needing it is Current = Voltage x wattage