How do 110V 60Hz North American phone chargers not burn out when plugged into 240V 50Hz European plug sockets (via an adapter, obviously).
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Because the whole job of those bricks is to change the voltage- from whatever the mains voltage is to 5-20V direct current (voltage output depending on what the device you plug in supports).
Since they’re converting the power anyway and these are global companies, it’s easy enough for them to make one conversion system worldwide (designed to handle up to 240V) and just stick different plug cases on them instead of building fully separate components for 120V and 240V countries. They could make separate chargers- the last one I recall that was 120V only was my Nintendo DS charger- but these things are so cheap to manufacture in bulk in may be more expensive to make the separate ones.
Because they are designe to handle both.
The common design is a switch-mode power supply where you first convert the AC to DC. Then you create a high-frequency AC by chopping it up and lowering the voltage with a transformer and then rectifying it DC and charging up a capacitor on the output.
The device measures the voltage on the output and controls the creation of the AC part. If you create an AC that is 50% of the time at 120V and 50% of the time at 0V the power of it is equal to one that is 25% of the time at 240V and 75% at 0V. The AC you create like that switches from on and of thousand of times per second.
It is the feedback where you look at the output voltage and control creating AC part that makes it possible to have multiple different input voltages. The AC signal you create is the one that delivers enough energy to keep the voltage correct at the output. The percentage of the time it is on depends on the amount of power that an attached device use,
You can control it yo if you should keep a water level in a barrel with a hole in the bottom. You have two hoses where one is a fire hose and one is a garden hose. You can control the water level with both hoses just by turning them on when the water level gets too low and turning them off when it gets to high, The time you have the fire hose open will be short compared to the garden hose but you can still do that.
The same principle applies to the power supply, it takes time to charge up the capacitor, and even if the output of the transformer differs you can keep the capacitor voltage correct by switching the input voltage on and off quiclty.
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