No offense but the 'only one power connector' is your least concern. Because i google it your pc specification and i couldn't find what psu is installed. This is why i would never buy or accept even as a gift a brand name pc, but that is another story. So, am very curios, who told you that your pc supports that graphic card? Because if Dell told you then it will work, but if some friend recommended you than it could be trouble. Just my personal experience and thoughts.
And another thing, even if it works, your cpu is not good for that graphic card (not good is very simple explanation)... And in the worst case scenario, you would need to change your psu, cpu, mb and who know what... In that case better sell that Dell and buy new pc... But again this is another story...