ATX Motherboard Power Connector
The ATX motherboard power connector was first implemented by Intel in the mid 1990s and has since become the standard for PC motherboards. The ATX power connector differs from the AT power connector primarily because it has 20 pins arranged in two rows of contacts in a single, rectangular connector, rather than a single row of pins.
The ATX power supply and motherboard power connector has since been modified to include a separate four pin connector (bringing the total pin-count to 24) that offers two additional sources of ground and positive 12 volts.
On the main connector, four special wires offer enhanced power control to ATX devices: Power On, Power OK, 5 volt sense, and 3.3 volt sense. These are used to keep voltages within 5% of their specified values. Negative voltages on the ATX motherboard power connector are acceptable within 10% off their stated values.
Dell ATX motherboard power connectors use compatible plugs, but may involve proprietary wiring that works only with a Dell-supplied power supply. Computer owners working with Dell computers should verify whether or not the power supply used with them is a standard ATX power source or if it is a proprietary unit.
ATX power connector image credit: Bruce Tyson
ATX power pin out image credit: Bruce Tyson