looked on google and i think i found my answer. They say the ones with 3 wires have the 3rd wire to show rpms you need a 4th one for speed control.Never knew that but now i know. and also im not sure but maybe my fan adjusts itself because it has a sensor connected to it. im guessing its the temp sensor so when it gets hot the fans work faster. Not sure but could be it as i read in some forums that some fans do that. I was wondering why it came with a sensor connnected to it. Because on the box it says from 600-1400rpms. like my cpu fan i can control that but theirs 4 wires. and im guesing its same if u plug it into the psu the fan gets power does but it doesnt show you rpms on your pc and its still dont go full speed assuming its because of that sensor which tells it how fast to go.
Could that be right?
if so how can i make the senor seem like its hot just so i can see if that effects the fan speed otherwise if thats not it i have no idea what thats for.