what are the differences between the old GFCI receptacle and the new NEC code approved GFCI?

Answer 1

With the new GFI's when the power goes out, you have to manually reset the GFI in order for it to function again. In fact, when you initially install one, and turn the breaker on, you'll need to reset it. When the power is out, the reset button will not function.

The benefit is that you are not able to hook the new ones up backward. The old ones could be wired in reverse and would function in a manner as to not offer GFI protection.

Answer 2

What do you think changed in the NEC?

There are some advances in the GFCI receptacles, but not mandated by code. One mentioned above is a GFCI will trip if wired incorrectly (line/load reversed at least). Another is GFCI's that "continuously" test themselves.

The other answer about tripping when power is lost is NOT true for GFCI receptacles (that would be a major headache for people). It is the case for portable GFCI's used in construction. They have to be reset after plugging them in.