Red is the 12 volt line, black is the ground, yellow is the control wire that lets the motherboard control the fan speed. If you hook up just the red and black wires the fan will run at full speed all the time.
As for amps most 50 and 60 MM fans run at 0.8 to 1.0 amps. and since most computer fans are 12 volts the wattage would be around 10-12 watts. Most of the fans run in the same range
Vantec 80 mm Tornado Case Fan Sleeved
* Dimension: 80X80X38 mm
* Rated Voltage: 12V
* Rated Power: 9.1 W
* Rated Current: 0.76 Amp
* Fan Speed: 5700 RPM
* Air Flow: 84.1 CFM
* Noise: 55.2 dB(A)
Just remember that:
Volts X Amps = Watts
A good multimeter would tell you what the voltage of the original fans are. A multimeter is also good for measuring amps too. Just something simple like this one. Buy one at your local Home Depot.http://www.multimete...com/dt830bf.htm
You talk about using a DC adapter to run these fans. What i have done is found a working 12 volt AC/DC adapter with 3 or 4 amps ( at the local fleamarket)and wired the fans directly to the wiring after cutting the plug off the end of the wiring. If you want only 2 fans look for a 2 amp adapter. When they matrch up the fan amps and the adapter amps the fans will run fine without overspeeding themselves. Too many amps on the adapter will speed up the fans to where they are running too fast as there is no diode's to regulate the power.