This led me to wonder why we still need the -12V supply - I know the -5V supply was removed a while ago because it was only needed for ISA slots. According to Wikipedia, -12V is for RS-232 ports and PCI slots, both of which are hardly seen on any current motherboards. It should be safe to use it for fans, but 7.2 watts is not very much power. Looking on Mouser, I see 24VDC fans that consume 1 watt or 18 watts depending on speed, so one could easily overload the -12V bus if they are trying to get a lot of CFM. I don’t see a compelling reason to use 24V fans in a PC.
From what I've read, ATX12VO really is 12V only; peripheral power connectors (sata/molex) will be connected to the motherboard, where the 5v and 3.3v (if needed) will be generated. 3.3V on sata power plugs was never reliably available and was rarely if ever used, and one of the pins was redfined to be a disable pin, so it's usually best for everyone if 3.3V isn't provided at all.
-12V for RS-232 is easily generated from +5V or similar sources; max232 chips have been available since the 80s
I'd suspect they'd go up to like 48V. It's the max voltage for USB-PD 3.1, which corresponds with being the effective highest voltage you can have before you're no longer "low voltage". This is also why PoE is approximately the same voltage.
People can easily overload 12V motherboard fan headers, too.
> if they are trying to get a lot of CFM.
If so, they probably have a PSU larger than the entry-level 350W unit I specified. Higher wattage PSUs will provide more power on the -12V rail as well.
> I don’t see a compelling reason to use 24V
Neither does anyone else. Still, correcting a bit of misinformation in the article.
