HD7750;
55 watt TDP, 400 watt psu reccomendation
GT430;
49 watt TDP, 300 watt psu reccomendation
Difference's in power consumption
http://www.techpowerup.com/reviews/HIS/HD_7750_iCooler/24.html
GT430 has a higher draw in Furmark and a much lower power reccomendation, go figure
Yes a 7750 will run on a 300w/19a oem psu