most fans have a "startup" voltage around 5- 7 V. this means that even thou its meant to go on 12 V at some RPM (for instance 2500 RPM), it will still rotate and push air on lower voltage, e.g. 7 or 5 V. You might have problems if the startup vltage is higher, but since it works - you are OK. Keep in mind that the CFM (and noise levels) will go down on lower voltage also you can easily hook up a 12 V adapter and use a fan controller unit (10$) like this and controll the noise/ airflow yourself
An easier solution would be to get a variable power adapter that does from say 2-15V and just select the appropriate voltage. They're about 10 bucks as well.
Being in england, things like this are hard to come by lol Its blowing a nice amount of cool air so im going home to my mums for a weekend visit and gonna rumage through my old pc stuff Thanks guys