Hi there,
Your gpu needs 400W so you can't experience power shortage with your current psu. There are certainly more reliable brands than Raidmax, for example corsair and thermaltake. It's not worth it to save on the psu either, since if it goes out usually almost everything goes with it.
As for how high you can go, nothing limits you, but there is no need to get a psu higher than 550 W for your current setup.