There are typically two types of pump:

1. DC (direct current)
2. AC (alternating current, mains power)

DC

Most DC pumps will be rated at 12volts and can be plugged directly into your computer's power supply for ease of operation

AC

AC pumps plug into wall outlets and will therefore continue running even after the PC is off. This problem can be easily remedied by installing a relay to turn the pump on or off based on whether the PC is on or off. This, however will require some work and knowledge of relays to be completed successfully.