The power supply is a pretty inexpensive component to replace in your computer. It’s fairly easy to replace a power supply also, it’s usually held on with a couple of screws. When removing the old power supply pay close attention to where the all the different plugs are plugged into for easy re installation.
PC Power and Cooling and Newegg are a couple good places to check power supplies online.
How much wattage do I need? An average computer will do pretty good with a 400 watt power supply, what you could do is check what your previous power supply wattage was, and replace it with the same wattage. This power supply calculator should be helpful check it out here all you have to do is enter a few computer parts from the drop down menu and it will give you a good idea the kind of PC power supply wattage you will need. If you are still unsure than bring the power supply to a local computer store and they will get you the proper proper power supply for your computer.