Definitely. The 500W power supply you have will be more than enough for the Gigabyte Radeon HD 7950 GPU, even if it were the OC model, or any other HD 7950 for that matter.
The Gigabyte HD 7950 requires two 6-pin PCIe power connections, which the Strike-X 500W has. The HD 7950 is a very efficient GPU, and a system under load would only pull around 400W with this GPU cranking along inside of it.
The Aerocool Strike-X 500W will be fine, so have fun with your new upgrade!