Kbase Article of the Week: Install MPX Modules in Mac Pro →

Apple Support:

Follow these steps to install MPX Modules in your Mac Pro. MPX Modules must be installed in PCIe expansion slots 1 and 3.

Important: Each PCIe slot is rated a maximum of 75 W; Each 6-pin auxiliary (AUX) connector is rated 75 W, and each 8-pin AUX connector is rated 150 W. Only install PCIe modules that specifically state that they are compliant with the industry standard PCIe specification. Use of noncompliant modules may not keep different input power sources separated, resulting in a possible burn hazard, and may damage the computer.