Most desktop computers operate on domestic AC power, but in some specialized situations, you might want to replace your computer's power supply with one that uses a DC power source. For example, a DC-powered desktop computer can be useful if you're using it aboard a boat or truck that doesn't have access to AC, or if you're obtaining power for the computer from batteries or solar power. DC power supplies that fit the same space in your computer case as the conventional AC power supply are available from several suppliers.
Before you replace the power supply in your computer with a DC supply, be sure you consider the alternatives, including a separate DC-to-AC inverter, and a laptop or other portable that normally uses DC power. A power unit for a laptop that plugs into a car's cigarette lighter or some other DC source is likely to be less expensive and more flexible than a desktop computer that can only run on DC power.
Whether you use a DC computer or an inverter, don't overload your power source or the wiring between the power source and the computer. You can't run a 250 watt computer and monitor through a cigarette lighter, or connect the computer to the power source with tiny wires.
And remember that in these situations you also need a monitor that can use DC power-they're out there, but they're not common.
If you do decide to install a DC supply in your desktop computer, simply remove the original AC supply, put the DC unit in its place, and connect the output cables to the motherboard, disk drives and other components inside the computer case.