Question

Why do all electrical appliances work on dc supply

Answer 1

Electronics cannot run directly on AC, it needs to be rectified and filtered to provide a smooth DC to power the electronic circuitry within the device with a constant voltage.

Answer 2

It highly depends on the "appliance". DC is cheaper and easier to produce, and is used for most circuitry (ICs, etc). AC is used in devices with transformers and large motors, because transformers ONLY work with AC and AC motors are more efficient than DC. It highly depends on the parts in the "appliance"