yes it will fit, however it will leave a gap around the PSU because of the difference in sizes between the Dell PSU and the standard PSU.
What do you mean?
From what i see the dell psu is an atx spec psu and should be the same size as the corsair psu (i think you mean this one when you say;"standard psu"?).Otherwise would the corsair not fit.
Why do you want the corsair?
Are you having problems?
Do you want to upgrade in the future?
The 305watt psu should be enough for the 7750,it doesn't need an extra power connector which the corsair would supply and i think 305watt should be enough for a basic system=motherboard+cpu+hd 7750+hdd+dvd player.