For those wondering what JK is referencing:
Voltage Over Current Limit (Iout limit)
+3.3 V 110% minimum; 150% maximum
+5 V 110% minimum; 150% maximum
+12V1 Peak current minimum; 20A maximum
+12V2 Peak current minimum; 20A maximum
+12V3 Peak current minimum; 20A maximum
+12V4 Peak current minimum; 20A maximum (22A maximum for 750W-800W)
IIRC later version of the spec removed the requirement for multiple 12V rails and with it the max current on the 12V rail.
Joel, I think what may be unclear Joel is that in the PSU linked above while the PSU has 6 PCIe connectors it puts TWO connectors on one strand of wires. So each pair of PCIe connectors is limited to 22A. With three pairs of PCIe connectors at least one rail will need to drive TWO PCIE connectors and thus the load on that rail is half of a Jupiter. To be clear this wouldn't be a problem if a PSU with four PCIe connectors connected each one to a seperate rail but for cost reasons they don't. If you look at the wiring of all ATX PSU you will find each set of cables has two PCIe connectors in parallel. So multi-rail PSU are going to be bad news.
However it isn't quite that bad. Later versions of the ATX spec removed the requirement for multiple 12V rails and today almost all high end PSU use a single massive (100A+) single 12V rail. It is cheaper, more efficient, and easier to manage. However despite all the connectors attaching to the same rail for safety no PSU is stupid enough to allow 100A to flow down one connector. 100 amps is a massive amount of power enough in a short circuit situation to cause a fire or death. So while technically a PSU can deliver 100A+ on any connector (PSU connector not downstream PC standard connectors) no PSU is allowed to do so. It is just a lawsuit waiting to happen to design a product than if a short circuit occurs will allow 100A+ to flow to wires and connectors not designed for that kind of current. All single rail PSU employ over current rotection at the connector level to prevent the full PSU current from unsafely flowing down one connector. They will trip if "excessive" current is going down one connector. It might be 20A, 30A, 40A all depends on the design and configuration. There is no way of just looking at the PSU what the limit might be. To put it into perspective the PCIe spec only require 150W per 8 pin connector so a set of wire with two PCIE connectors in series "normally" won't pull more than 25A.
Lets imagine a Jupiter pulls 790W (65A @ 12VDC) that means the current at each PCIe connector is 16.25A. No problem there. However if there are two PCIe connectors on a single "strand" and both are used then the current on the strand is 32.5A. If the overcurrent protection for the connector is 40A well there is no problem but if it is 30A?
Thanks for background info, very appreciated!
So I guess the corsair is quite a good choice:
* dedicated single +12V rail with user-configurable virtual "single rail" and "multi-rail" software modes
* features a massive 71.6 Amp (859.2 Watt) single +12V rail
* can also be configured as a multi-rail device with individual PCI-E over-current protection (OCP) trip points
=> http://www.corsair.com/us/blog/ax860i_technical_details/