Thanks! Yes, the fan inside the power supply is regulated. I just looked up some technical data of fans of the same size as they are built in the controll box of the CR 10. In total they draw about 0.3-0.4 amps at full power. The fans I would use together with your fanbase would draw about 0.5 amps in total. So I think it's not a problem to connect the directly to the power supply of the printer.
I found some fans with a integrated temerature sensor, I guess that coud be a perfect match for the fanbase.