A cheap system doesn't need much more than 50 watts baseline (an MSI Z77A-G45 motherboard, 4GB ram, hard drive, and celeron G530 only used 27 watts for me at the wall), and the R7 270 likely won't use much more than 175 watts under load. I have kill-a-watts and I've measured power output of comparable cards. Gigabyte is wrong.
OK Thanks. If I add more cards, I should use risers, correct?