In Figure 18, you can see Galaxy 1000 W label stating all its power specs.
As we already explained, this power supply has two separated power supplies inside. The +12V1 and +12V2 rails are connected to the first power supply, while the +12V3, +12V4 and +12V5 rails are connected to the second one.
According to the label the first power supply has a limit of 408 W (34 A) while the second one has a limit of 492 W (41 A). This is funny because internally the two power supplies are completely identical, so they have, in theory, the same limits. These numbers, however, probably express the levels where the power supply protections were configured.
Because the +12 V outputs from the two internal power supplies don’t talk to each other, their maximum power cannot be added.
For better power distribution and efficiency the two power supplies should be delivering more or less the same amount of power with the system running. However, unless you have a multiprocessed system this won’t happen. Video cards tend to pull more power than CPUs and thus the internal power supply that has the video cards connected to tend to be more loaded than the power supply were the CPUs are connected to.
Unfortunately we don’t have the necessary equipment to make a true power supply review; we would need to create a real 1,000 W load to check if this power supply could deliver its labeled power or not.