You have a very weird build. FIrst, that power supply will not power that graphcis and your components. Also, that GPU will probably not fit in that case, the case only supports cards up to 30mm.
The case supports graphics cards up to 310mm long. The Sapphire Radeon HD 7950 is 270mm long.
There is a small risk of a clash between the GPU and the PSU, but since the PSU is shorter than 160mm it should be okay.
And the 550W PSU actually is sufficient for the build.