yes. it will be enough for 650ti boost on SLI.
here is a reference build with approximate power consumption which is like 480W, so 550W should be enough. Just make sure its a quality brand (Seasonic will be a good option) which provides stable voltage and current under high load. just wattage information is not enough to decide if the psu is good or not.
It is recommended to have a 600 W psu for sli'ing those cards. Also, if you are planning to oc, you might want to consider something slightly larger (650W - 750W) depending on how heavily you will be oc'ing.