The Antec and Corsair PSUs are both decent and should be fine for 570 SLI.
Review of GTX 570 SLI here:
http://www.guru3d.com/article/geforce-gtx-570-sli-review/1
Review of GTX 570 SLI here:
http://www.guru3d.com/article/geforce-gtx-570-sli-review/1
GeForce GTX 570 in 2-way SLI
A second card requires you to add another ~225 Watts. You need a 750+ Watt power supply unit if you use it in a high-end system (800+ to a KiloWatt is recommended if you plan on any overclocking).