I think I know the answer to this question, I just bought a new scope Owon SDS7102 and I'm just experimenting. I thought all DC that comes from an AC signal was pulsating DC or a square wave. I hooked my 5.3 volt wall wart up to my scope and my max voltage was 5.3 volts, but my peak to peak was 300mV. Comparing this to my scopes 5V square wave reference, the signal from the charger is much much smaller. Is this because it's not a square wave but constant voltage? I guess this makes sense when I think back about how rectifiers work and how the capacitors smooths out the wave form. I guess I'm just looking for extra validation. If constant voltage similar to a battery is so easy to attain, then why are square waves so popular in the lab? For learning purposes? Stupid question?