Way over kill!

Totally ok to run a PC fan at a lower voltage.it will use less current. The wall wart suggestions are the cheapest and easiest as you probably have one laying around. I'm an ee and do this all the time. It's actually hard to find a 12v wall wart that is less than 1amp these days. A 5v cell wart will run it silently but with much less air flow. I use this combo for my bench fan for soldering to keep the fumes out of my face