The potential is there, for the voltage at least. A rather large bank of 9 volt batteries in parallel could potentially run a PS2, but an induvidual one? No chance. It's a matter of current drain. The PS2 may run on 8.5V, but notice the power adapter also outputs at 5.65amps? A single 9volt cell would have, on average, around 450mAH or so. So while you have the voltage there, there's nowhere near enough power.