It is possible that all the information you need is not going to be on the fans, or the chargers. Do you know how many watts the fans use under normal use? The voltages they are rated to run at? Or the resistance of the chargers (in Ohms, or the Omega symbol) If so, you can get a concrete answer.
It would be better to say that you should be safe to run 2 PC fans up to 120mm fans off of one 12V adapter. The lower the voltage of the adapter or the more fans you put on (which will increase resistance), the slower the fans will run. So you should probably only need two more adapters to power all of your 3 new fans at half speed, or you can put a 12V adapter on each one to for top speed, or mix it up to fit your needs.
Hope this helps a little.