How can I convert A.C supply into D.C. supply?

There are two methods of doing it

  1. Ac motor to DC generator coupling
  2. Rectifiers

You couple the axis of a AC motor with the axis of DC generator. So the AC motor generates torque and rotates the axis of DC generator which generates DC power.

The other method is use of rectifiers. There are two types of rectifiers half wave and full wave. Full wave rectifiers are more effecient but you cant control the output. To get a controlled output use AC-DC converter.