How do i find out my computer's power supply?

open up the case and look at the power supply (the rectangular silver box where the power cord connects to) and find it's wattage (should be between 250 and 600 watts). The more peripherals you have in your case the more watts you need. The graphics card might have a recommended size as well. If the power supply is too small, buy a bigger one and install it - it's rather straightforward. Make notes on what you unplug from the old one so that you reconnect everything with the new one