How does a circuit regulate current in response to a lower voltage?
Imagine a universal power supply that works in multiple countries that have different mains voltages, just like the one that is used to charge a mobile phone. Let's assume the phone requires 5V at 1A so it draws 5 watts of power when charging. Let's also assume the power supply is made of unobtainable ideal components so it does not consume power itself, so it will always take 5 watts from the mains socket when charging. So as power drawn by the supply is constant, it means it draws double the current from a 110V mains socket than it would from a 220V socket.