How do devices control how much power they use? In power systems (Australian for reference) the grids run at a constant voltage of 220V. I’ve heard of switches were less voltage being used is created by adding more resistors for example to dim light bulbs. But for more advanced appliances such as a PlayStation 4, there’s a rest mode that uses significantly less power. How do electronic devices use less power without needlessly wasting it using resistors? Sorry if this is a basic question I am only in my preliminary year.
 A: Start by thinking about how electronic devices use power at all. Where does the power go?
Well the power usually goes through a "power supply unit" containing some power converting circuits that turn the high-voltage AC into low-voltage DC. Then it goes to a bunch of computer chips that are all in parallel. And some other circuits, also in parallel. Everything is connected to the power supply in parallel.
In parallel? That means if we turn off some of the chips or circuits, the total resistance goes up! It's not adding resistors in series, it's removing resistors in parallel.
In reality, it's quite rare to turn an entire chip on or off, but it's quite common for each chip to have circuits inside it that can turn parts of the chip off. Then, power saving mode is when most of the parts that can be turned off are turned off. Of course it's not limited to chips, it's just that most of the interesting stuff in modern electronics happens inside chips.

Even dimmer switches don't work by adding series resistance any more. They work by turning the lightbulb on and off repeatedly. You can see that a 0-ohm resistor doesn't waste any power (because voltage is 0) and an infinite-ohm resistor also doesn't waste any power (because current is 0). By alternating between 0 and infinite ohms the dimmer can adjust the amount of power that goes to the lightbulb without wasting any. We don't think of an 0/infinite-ohm resistor as a resistor - we think of it as a switch.
