Heating nitinol rod using AC/DC power supply

You need to reduce the output voltage of the power supply you are using (the power supply is going into current limit which is probably not very good for it at all). The rest is simple ohms law (and a bit of trial and error to get the right power to give 80deg C). Try a lower voltage or variable voltage power supply (after you figure out what the value of resistance of the rod is).

Here's a trick I used to test circuit breakers one time. If you can obtain a current transformer (http://en.wikipedia.org/wiki/Current_transformer) you can energize the output coil with low voltage AC. Make a closed loop including the Nitinol wire pass through the core of the current transformer. If you figure out how much current you need, current transformers are usually rated as output voltage vs input current. Just reverse the relation.

One way to go about this is to use a lower impedance supply. You can heat the rod with DC, but the supply will cost more than heating it with AC. An arc welder supply or even a spotwelding transformer should do a good job. In any case, the supply you are using is not appropriate. Adding a resistor in series just increases the supply impedance and makes things worse.