# Can we get more current by reducing voltage on a power supply?

This is very basic question but I seem can't find the answer. All out there is theory, but no practical explanation about this.

Assume I have a 10V 2A power supply. So in theory it outputs power of 20 watts. Now if I reduce the voltage to 5V with a 5A capable buck converter, can it output the same 20 watts? If so, 5V will use 4A to achieve that.

In general, can we increase the current by reducing the voltage in a power supply?