Seasonic's X-650 PSU is fully modular, allowing you to choose exactly what cables you use though the ATX power is mandatory.  It has four 6+2 PCIe power connectors and can deliver 648W @ 54A to the 12V rail making this a solid choice for a multi-GPU system.  The performance on [H]ard|OCP's test bench was excellent, the only complaint they've had is that Seasonic really hasn't changed much about their PSUs in quite a while.  That might be a little boring for reviewers but for enthusiasts, great performance at a variety of wattage is a good thing.

"Seasonic's X-Series computer power supply comes to us boasting a patented fully modular design that minimizes voltage drops and impedance while greatly maximizing efficiency, cooling, and overall performance. Being a Seasonic unit, we can also count on it targeting the users looking for a quiet computing experience."

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