Power rating The overall power draw on a PSU is limited by the fact that all of the supply rails come through one transformer and any of its primary side circuitry, like switching components. Many of the early DC/DC converters converted 5 volts into the lower voltage. The regulator controls the switching transistors insulated by optocouplers or pulse transformers. When the newer ATX standard was created, a 3.3 volt rail was added to power the newer chips. So a PC of the time had a mix of 3.3 volt and 5 volt chips directly connected to their respective voltage rails. Their power supplies also provided -5 and -12 volts but those only delivered small amounts of power. Devices that run on voltages other than these directly must then be indirectly powered through on-board voltage regulators, which take the 5 V or 12 V from the power supply and convert that to the lower voltages required by various components.
Remove the resistor and then cut the excess wire away so that after reinserting the wire it will not exit the other side. These power supplies were generally not capable of power saving modes such as standby or «soft off», or scheduled turn-on power controls. Modern personal computers universally use switched-mode power supplies.
Many modular supplies have some permanent multi-wire cables with connectors at the ends, such as PC main and four-pin Molex, though newer supplies marketed as «Fully Modular» allow even these to be disconnected. Modern video cards also have their own converters on the card which convert 12 volts into the desired voltages. Recent power supplies have a standby voltage available, to allow most of the computer system to be powered off. Older PSUs deliver most of their wattage on 3.3 and 5 volts and newer ones deliver most of it on 12 volts. They had a 5 volt rail because that was the voltage needed to power most of the standard silicon chips of the time.