The JonnyGURU reviewers know what they're talking about, and with test number 5 in the Hot Box the 12V rail is pulling 37A, which is more than enough for the R9 380. You will be fine with that power supply.
The ripple suppression isn't "Take a picture and frame it" quality but it's decent. That should be your biggest concern.
I don't know what makes a power supply good. :P I just look for reviews and do a little research. I like computers and tech, but it won't be my profession later. Thanks a lot for the help and info~