How to convert 120 Vrms AC to 5 V DC (like AC to DC conversion for a USB charger)

This video demonstrates a rudimentary circuit animation for converting from 120 Vrms AC to 5 V DC (like AC to DC conversion for a USB charger). The falstad circuit simulator is used to demonstrate.

Below is the basic script:
o the goal is to get about a constant 5 V DC output here from the usb side, but the challenge is we are plugging this directly into the wall at 120 Vrms.

So let's go ahead and do a rudimentary model of this in falstad.

So we have our AC source here. Notice it is maxing at 170 V because it is coming in at 120 Vrms

Now if we look at the voltage across our load here, it is the same thing, because they are directly connected.

This is not quite what we want coming out of the usb side, right, so the first thing we do is add a transformer.

Now this transformer has an a value of 29 so it is reducing the voltage across our load down to a little over 5 V, so that's the first step. But we want DC here so the next thing we can do is get rid of the negative voltage by using a 'rectifier', which only allows current to flow in one direction. For this, we'll use a 'diode'.

OK, so this diode only allows current to travel in one direction. So it doesn't let the current go backwards through it. So the current is only traveling top to bottom through our load, so there is only a voltage drop from top to bottom across it. So you can see in this plot down here that the diode basically cut off the negative portion of our input AC signal.
You may imagine it would be more efficient to invert that negative voltage instead of losing it, and we could do that with a more complicated setup of diodes like this.

So you can see this setup inverts those negative voltages and would be more efficient, but let's just stick with our simple setup here for the sake of simplicity.

So back to this setup, we want a constant voltage, not something going up periodically like this. So next component we can add is a capacitor.

So now we through in a capacitor in parallel, and this helps us out a lot, because you can see the voltage across our load is pretty flat now, just above 5 V. But how did the capacitor do this? Well you can tell by looking at the current.
When the diode lets a pulse of current through, that current is going mainly to the capacitor to charge it up.
When the diode is not letting current through, the capacitor is discharging into our load.
So that capacitor is periodically charging and discharging, allowing a fairly constant current flow through the load, which you can see, stays at a relatively constant voltage.
To flatten that further you could use a regulator to sort of shave off the top of the curves.

Now this is a very rudimentary AC/DC converter, and there's lots of other components to a real AC/DC converter to make it more effective and efficient, like that more-complicated diode setup.