[formerly_proven]

It recognizes how things are already. The 5 V and 3.3 V step-down converters in the PSU are pretty much only for Molex/SATA-connected peripherals, and those don't use 3.3 V anyway (99.5 % of them), since it's not guaranteed to be there. So the 3.3 V rail is pretty much pointless. 5 V not quite as much, but even in an enthusiast-level PC there will be probably just a handful of things actually connected to that - most likely SSD/HDD and maybe something like a fan controller.

No heavy loads are connected to the 5 V / 3.3 V rails. Those are all supplied through the 12 V rail.

[toast0]

> The 5 V and 3.3 V step-down converters in the PSU are pretty much only for Molex/SATA-connected peripherals, and those don't use 3.3 V anyway (99.5 % of them), since it's not guaranteed to be there.

Yeah, not only is 3.3V not guaranteed to be there, the latest rev of the SATA power spec reused (at least one) of those pins as a signal to inhibit spin-up; used for power sequencing in large disk arrays, with the fun side effect that if you've got a PSU old enough to have 3.3v on sata power, and you use a hard drive new enough to support spin-up inhibiting, you need to either tape the pin, or cut the orange wire, or you can't use your disks.

[dhdc]

I am pretty sure M.2 uses 3.3V exclusively, and depending on the implementation, RAM sometimes gets its power from down regulated 3.3V as well.

Though you do have a good point, nobody misses -12V and -5V.

[formerly_proven]

Yes, there's actually a lot of stuff that uses 3.3 V, e.g. anything connected to smbus. But none of them connect directly to the PSU, so there is no need for the PSU to do it.

[jlgaddis]

> nobody misses -12V

Some of us (masochists) actually like RS-232!

[whatevaa]

I remember reading about some people adding so much RGB stuff into their system to actually run into current (A) maximums on power supply 5V rail, so there might be some exceptions, though not many.

[pantalaimon]

USB is also 5V