again, i dunno about the inspirons but i got a dimension e510 and e520 and you can replace the Power supply with a better, standard, one, enabling you to run more powerful cards.
Also the stock dell psu doesnt have the connectors better cards need
You can replace the PSU in dimensions with a standard better one, so i *think* the inspiron can, but its a tight fit and there is some cutting of the mesh at the back required in some cases.
long or wide cards wont fit in dell pcs, by the way.