There's more to consider than just the wattage (which you've underestimated anyway), there's amperage as well which is equally important.
gtx560ti - 170W
AMD A8 - 100W
Each hard drive - 5-10W
SSD - 5W
Wireless card - 1-5W
Sound card - 5W
Not to mention the RAM, all the motherboard's innards (like the SATA controller and the BIOS and the dozens of other controllers for ethernet, USB, firewire and so on), the fans, and powering that headset, mouse and keyboard, plus any other random peripherals that the computer is powering (like charging mobile devices).
Another reason that you'll want something with a higher wattage is that it doesn't actually have enough connections to plug in everything you want to buy (the GTX56 Ti needs two PCI-E connectors - that current PSU only has one).