SO im lost my psu max is 264watts? wth. Its supposed to be underrated.
Sorry for late reply, have some stuff to test
There are peak specs and continous specs. It depands what your PSU is specified.
Most of the time it goes like: you can do 600W, when you do 180W on 3.3+5V and 410W for the 12A rails.
So, 10W are left for +5Vusb.
The 12A rails would be rated as 22A per rail, two rails = 2x 22A = 528W... but you can do the 528W only, if your mainboard does not use more than 62W on the +3.3V & +5V rail which is of course not working. So don't get confused with the specs on your PSU. It's not that easy. Of course 12V rails also means they count CPU in.
Peak vs. Continuous:
Every PSU can sustain higher amps for a short time, mostly about 30 seconds. If this time is exceeded the PSU will shut down. Continuous means the PSU can hold the specified output always.
Your PSU is rated 264W for the 12V rail(s) only. You can make a picture of the label with the specifications on your PSU and I can tell you more about your PSU.
Here an example of the Seasonic S12II 330W:
combined power: +3.3V & +5V: 120W
combined power: 12V: 288W
So, 288+120 can not work... because the PSU is rated with 330W
Also 3.3V x 18A = 59.4W, 5V x 20A = 100W, total is 159.4W does not work either.
So it can use max. 18A on 3.3V but not at the same time 20A for +5V, the maximum in this case would be 12A for +5V.
If your board/equipment is using 120W on the +3.3V & +5V you can't use 288W for 12V... I guess this can only be happen on crappy ASRock boards where no ATX 2.x power connector is used. +5Vsb rated 12.5W is used for USB devices when the computer is off, so it does not count in the active state.
Have no idea what equipment is using the -12V, but it's reserved when the computer is running.
Totally you have about 320W to use.
A harddisc is using about 0.5A for 12V and about 0.8A for 5V
A mainboard is more complicated, the voltage for the memory can be generated from 3.3V, 5V or 12V rails, this is up to the engineers, but like the CPU 12V is the best guess, because it is more efficient. 1GB stick is about 4W, overclocking is increasing it. Most chipset/onboard chips are running with either 3.3V or 5V. A board should use about 30W.
So you can do some calculations yourself