While I don't know the exact component that needs 12V, you have to keep in mind that your typical computer draws about 300W under a small load. 300W/12V means 2

While I don't know the exact component that needs 12V, you have to keep in mind that your typical computer draws about 300W under a small load. 300W/12V means 25 amps. Reduce the voltage without lowering the power consumption and you need bigger wires to handle the increase in amps.