It depends on computer to computer, but let's say the max is 800W. It will take whatever it needs. If your keyboard consumes only 5W, obviously giving your keyboard 800W will blow it up.
On each Hard-disk, CD-Player, Component of your computer you will find information in as to how many watts of power they consume.It may be printed on components but more typically in the user-guide...
Your power supply unit, PSU. Takes AC power and distributes so much power to each connector. Each PSU, depending on the wattage of the unit gives each connector so much voltage. Each connector is...