It's blinking of the lower 1/3 or half of the Dell U2713HM display, lasting about 1 min, with different intervals; sometimes longer, sometimes shorter, ~5-10 min. Now I take out the GT620, using the integrated Intel HD 2000, never blinks. I'll try to upload some video later. Thanks a lot!
GT 620 consumes less power than HD 7750. Also, it should run on your computer without any problems. Could you describe the "blackouts"? We could maybe resolve them.
The only real alternative that uses less power is GT 610.