I think what Mark is getting at is the difference between a "linear" power supply (what he calls a "transformer based" or conventional AC-DC converter), and a "switching" power supply (what he calls an electronic converter).
Every device besides simple light bulbs, heating elements, and such that plug into the wall require at the very least: "isolation". Simply because it is much safer. Essentially it makes it safer because if the transformer is rated at a certain power level will break when that power level is surpassed, as is what could happen in a dead short. See if you shorted the hot and neutral wires (the two slots) with a conductor, you are looking at 120V (in the USA) / 0.5 ohms (the wire) = 240 amps of current. That 240 amps X 120V = 28,800W available instantly from the wall. Your talking about half a second or longer until your mains breaker or fuse melts. That much power will melt your house wiring, and quite likely cause a serious fire, not to mention can kill you. The purpose of isolation is to make sure that it is much less likely to happen. Any shorts beyond the isolation transformer cannot supply more than the rated power of the transformer. There are other reasons as well, including reducing the likelihood of radio frequency interference.
That said, the block diagram for a switching supply looks something like this.
mains -> transformer (most are step down, every one uses some kind of isolation)-> rectification -> smoothing -> high voltage DC -> PWM (pulse width modulator) (a small transformer is almost always here) ->output transistors -> high frequency high voltage AC -> rectifier -> smoothing. The output voltage is fed back to the PWM to determine the PWM duty cycle. higher duty cycle means more available current to develop across the load to maintain voltage.
Switching is very rarely used in your typical wall wart box plug. It is very common to see a switching supply in laptops and every computer has a switching supply.
Back on point - Every wall wart will use a few milliamps of power. There are almost always "bleeder" resistors that drain the output capacitors when there is no load. These are across the output caps, and sometimes also the input caps. They are high value and as long as its plugged in, will consume power.
In a switching supply, you use very VERY little power, since as long as there is no load, the PWM is essentially off. The only losses are leakage on the input circuit, and whatever power it takes (microamps) to keep the PWM on.