Unless you want to change that psu.
Send the quadro back.
Shop for a gtx 750ti.
That should run with no need for pcie power cables and give a nice bump in video power.
I have A Dell Inspiron 580. Older computer, but runs very nicely with an upgraded SSD. It came with a ATI Radeon HD 5450 which is a very low end graphics card. I tried to install a Nvidia Quadro 4000 but noticed I didn't have any extra power ribbons. What are my options at this point? Do 'better' Power Supplies have more cords coming out, or am I missing something very obvious here?
Thanks in advance for your help. I consider myself intermediate level with these things, but let me know if I'm missing any valuable information. Thanks!

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