GeForce GTX 570
On your average system the card requires you to have a 600 Watt power supply unit.
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).