Whenever I throw away any electronic item, I always keep the DC wall adapter just for this kind of purpose. They always seem to come in handy. Just buy a fan and note the voltage/amperage requirements. Then buy or reuse a DC adapter with those specs. You can buy universal ones also. You set these with switches. I know most fans will run off lower voltages, but you should know this can be a small fire hazard. The adapter circuit will run maxed out all the time and could overheat.