page_title: Power supply unit (computer)
section_title: 12 V–only supplies
hierarchical_section_title: Power supply unit (computer) / Development / 12 V–only supplies
context_page_description: A power supply unit converts mains AC to low-voltage regulated DC power for the internal components of a computer. Modern personal computers universally use switched-mode power supplies. Some power supplies have a manual switch for selecting input voltage, while others automatically adapt to the mains voltage.
  Most modern desktop personal computer power supplies conform to the ATX specification, which includes form factor and voltage tolerances. While an ATX power supply is connected to the mains supply, it always provides a 5 Volt standby voltage so that the standby functions on the computer and certain peripherals are powered. ATX power supplies are turned on and off by a signal from the motherboard. They also provide a signal to the motherboard to indicate when the DC voltages are in spec, so that the computer is able to safely power up and boot. The most recent ATX PSU standard is version 2.31 as of mid-2008.
context_section_description: Since 2011, Fujitsu and other tier-1 manufacturers have been manufacturing systems containing motherboard variants that require only a 12 V supply from a custom-made PSU, which is typically rated at 250–300 W. DC-to-DC conversion, providing 5 V and 3.3 V, is done on the motherboard; the proposal is that 5 V and 12 V supply for other devices, such as HDDs, will be picked up at the motherboard rather than from the PSU itself, although this does not appear to be fully implemented as of January 2012.
  The reasons given for this approach to power supply are that it eliminates cross-load problems, simplifies and reduces internal wiring that can affect airflow and cooling, reduces costs, increases power supply efficiency, and reduces noise by bringing the power supply fan speed under the control of the motherboard.
  At least two of Dell's business PCs introduced in 2013, the Optiplex 9020 and Precision T1700, ship with 12 V–only power supplies and implement 5 V and 3.3 V conversion exclusively on the motherboard. Afterwards, Lenovo M93P adopts 12 V–only PSU and performs 5 V and 3.3 V conversion exclusively on the IS8XM motherboard. 
  In 2019 Intel released a new standard based on an all 12V design, ATX12VO power supply only provides 12 V voltage output, 5 V, 3.3 V powers, as needed by USB, hard disk drive and other devices, are transformed on the motherboard, ATX motherboard connector is reduced from 24-pin to 10-pin. Called ATX12VO it's not expected to replace current standards but to exist alongside it. At CES 2020 FSP Group showed the first prototype based on the new ATX12VO standard.
caption: Connector ATX12VO