With the 500ohm load even the signal diode model should approximately mimic a better rectifier diode under higher load. I just used the 4148 because it was the first diode on the model list, the load is only 20ma's RMS. Just saying he's going to have one hell of a time figuring the difference between a 9VDC and 9VAC voltage source to his device. Likely because the only thing I can think of that commonly uses an AC wallwart are cheap cordless power tools, they could care less what voltage they get really, just as long as the new supply isn't capable of providing too much additional current. AC or DC wallwart's are typically current limited to the inductive coupling/capacity of the initial transformer stage, which is going to be the same from one device to the other. The bridge rectifier just happens to be on the device in his case which saves a few cents per device for the maker of the device as it's probably almost incidental to add a bridge rectifier to the device, a secondary power supply manufacturer is going to add a markup to the rectified output as opposed to an AC one, just because they can.