I am asking this because I was under the impression that these devices were supposed to ALWAYS be at either 0 volts (no output power) or 5 volts, regardless of how much current is going through them
If you think logically about what would be required to construct a device that behaves that way, you will see that such behavior is impossible to achieve.
Consider:
Your device starts out at 5 V and supplying 100 mA to the load. Good so far.
Now the load increases and the current exceeds the capability of the supply.
In response the supply switches off. It is now providing no output (0 V), and consequently no current and no power. This is what you have asked for.
Later, the bad load is replaced with a good load that only desires 100 mA again.
The supply does not know this, and cannot know this (it has no current to measure at 0 V, 0 A and no way to know what you have done outside its terminals). So the supply remains switched off.
One way out of this problem is for the supply to automatically try switching on again and see what happens (but how often, at what frequency?). If it does this, the heavy load is likely to see ON...OFF...ON...OFF...ON...OFF... The load may like this far less than a low voltage situation.
The other way out of this problem is for the supply to have a manual reset button. After it switches off a red light comes on, and you can press a button to switch it on again. If you try switching it on with the heavy load attached it will switch right off again, and now a typical user may be puzzled and confused--why won't the supply stay switched on?
So ultimately, one does not design things this way unless there is a safety concern (as with a GFCI or an RCD). The normal approach is to provide a graceful decline in voltage as the load gets too much. No funny business, no cutting out, just a smooth response. This is how your supply behaves, and how 99% of similar supplies on the planet behave.