Is this enough for a Gigabyte Radeon R9 270?

Solution
So what are the amps on your +12 volt rail? The red switch is for voltage selection is bad news. Every Google search I do for Kentek Black 550watt 12cm fan comes up with the same.
Yeah, it should even supply room for you to overclock it but I wouldn't as that PSU seems really shoddy, has bad reviews and can break down any second. If it does break down, it may short out the rest of your pc, so I would upgrade my PSU if i were you.