geofelt :
A single normal pci-e slot will supply a max of 75w.
That is why aux power is needed for strong graphics cards. A 6 pin connector can supply 75w, and a 8 pin connector can supply 150w.
There might be a limit of 300w for all if the pci-e slots, can you tell us where you saw that limitation?
I think you are ok with a sufficiently strong psu.
Pugetsystems.com , "As this is a server motherboard, some desktop features are not present: standby/sleep functionality is not guaranteed, and this board does not support the "Hibernation" feature built into Windows. SATA ports do not support hot swap. Video card support is limited to cards under 300W max."
The system specs for the system im ordering are :
Motherboard: Intel S5520SC
CPUs: TWO Intel Xeons X5690 3.46GHz SIX CORE 12M L3 Cache (will have two on 1 board)
RAM: 96GB Kingston DDR3-1333 ECC
Graphics: NVIDIA GeForce GTX 590 3GB
Sound Card: Creative X-Fi Titanium Fatal1ty Pro PCI-E
Wireless: Asus PCE-N15 Wireless 802.11b/g/n PCI-E Adapter
1st Hard drive: Intel 520 480GB SATA 6Gb/s 2.5inch SSD, Read: Up to 531 MB/s, Write: Up to 315 MB/s
2nd Hard drive: Intel 320 600GB SATA II 2.5inch SSD, Read: Up to 270 MB/s, Write: Up to 220 MB/s
Disk drive: Asus 12x Blu-ray Burner SATA (black)
Case: Antec P193 V3
Power supply: Silverstone ST1500 1500W Power Supply
CPU cooling: 2X Puget Hydro CL3 Liquid Cooling System
Mods: Custom 120mm Side Panel Fan