For either geosynchronous or low earth satellites, the power put out by the satellite transmitter is really tiny compared to that of a terrestrial radio station. Your favorite rock station probably boasts of having many kilowatts of power. By contrast, a 200 watt transmitter would be very strong for a satellite.
The satellite must generate all of its own power. For a communications satellite, that power usually is generated by large solar panels covered with solars cells.These convert sunlight into electricity.
Satellites must also be prepared for those periods when the sun is not visible, usually because the earth is passing between the satellite and the sun. This requires that the satellite have batteries on board which can supply the required power for the necessary time and then recharge by the time of the next period of eclipse.