The -12V rail, while historically present in PSUs, has become less important in modern PCs. Originally, the -12V rail was used to provide power to certain legacy components such as serial ports and older audio hardware, which required negative voltage levels for communication. The -12V rail was most popularly used in RS232 serial communication, one of the pins of the original PCI (not PCIe) slot and was used as a reference voltage in some audio hardware.
An example of a serial port.
However, with the evolution of PC hardware and the phasing out of older technologies, the need for the -12V rail has diminished significantly. Considering -12V became an optional integration with the introduction of ATX 3.0 PSUs and newer PSU design guides from Intel, most modern motherboards and components no longer require or utilize the -12V rail. As a result of the -12V rail being redundant, our RMe Series PSUs do not have one equipped. Users may find that if they test specifically for -12V, a failure status may be given due to the fact there is no -12V rail. This failure is nothing to worry about, though, as the chances of your build containing anything old enough to require this rail are slim.
With the increased power demands of certain components such as graphics cards, we prioritized designing the RMe Series to be equipped with a stable and reliable 12V rail, and given that the -12v Rail is largely obsolete, we've omitted it entirely.
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