For a system using a single GeForce GTX 660 Ti graphics card NVIDIA specifies a minimum of a 450 Watt or greater power supply that has a combined +12 Volt continuous current rating of 24 Amps or greater and that has at least two 6-pin PCI Express supplementary power connectors.
Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Total Combined Continuous Power/Current Available on the +12V Rail(s) @ 45-50°C ambient temperature, is the most important factor.
The XION Gaming Model 700W (XON-700P12N), with its combined +12 Volt continuous current rating of 36.8 Amps and with two 6-pin PCI Express supplementary power connectors, is more than sufficient to power your system configuration with a single GeForce GTX 660 Ti.
The JonnyGuru link, that @rolli59 provided, is for a different model than the OP has. JonnyGuru reviewed the XON-700P14N which has four +12V rails with a claimed maximum combined rating of 600W (50A).
The OP's XON-700P12N only has two +12V rails with no claimed combined +12V rating but it is actually 442W (36.8A). This points to an old obsolete design.