I'm planning on buying r9 390...it's pretty expensive and I'd rather not buy a new PSU if I don't have to. I don't do overclocking or anything...but I do play a lot of video games.
I would honestly consider getting another PSU. The EVGA B2 is on sale without mail in rebates on amazon for 57 bucks. Its an amazing deal.
No, that is not a good PSU at all and is definitely not safe for this build.
Also, your CPU is going to bottleneck the 390 badly in most CPU heavy games.
You will need a new psu, that one is bad to say the least, I would recommend getting something good like a Evga B2 or a Evga GQ or go big and get a Evga G2. Also don't get the Asus Strix, its a hotting running card, I would recommend a MSI Gaming.
Okay, I'll just build from a new CPU