Thermaltake VGA Power Supply Compatibility with Workstation T7400

I have a dell workstation T7400. The installed power supply does not have the proper connectors for the two new graphics cards I purchased. So, I bought a Thermaltake VGA power supply (W0157RU). http://www.thermaltakeusa.com/Product.aspx?C=1247&ID=1543#Tab0. This power supply is installed in addition to the main power supply. It installs in a 5.25 drive bay and has a separate power cord.

Unfortunately, I am having compatibility issues. The power supply comes with a bridge cable between the main power supply and the motherboard. I installed the bridge cable and by itself it works fine. However, the purpose of the bridge cable is to attach a molex two pin connector (coming out of the motherboard end of the bridge cable) to the Thermaltake VGA power supply, so that the Thermaltake power supply can know when the computer is turned on or off.

When I plug the molex connector into the Thermaltake power supply, the power on the main power supply shuts off (or doesn't turn on) and the amber 1 and 3 lights start flashing.

Does anyone know the issue here? Or how to solve it?