As the power transmitted depends on the speed (until you have reached the maximum you can produce, in other word, you get to the hyperbolical part of the v/t diagram), it is not possible to make a direct correlation between tractive force and power rating.

What matters is the coefficient between tractive force and axle load. Even the worst tap changer electrics had average coefficients around 0.25 under "normal" conditions. Getting a train moving when it just started to rain, or with leaves or larch needles on the track requires then a lot of skill by the engineer. Modern locomotives with micro-slip control and accordingly set up software can reach a coeffiicient of 0.35 or even better on dry rails, and not that much less on wet rails. Most locomotives are, however, not fully use the micro-slip range, because that makes the wheels screech.

In order to adjust the software, the manufacturers run tests under kind of standardized conditions (always the same stretch of line, dry rail, wet rail, greased rail (greased with a standard grease), etc.). To play in the top league, a 4 axle locomotive with around 20 tonnes of axle load has to be able to get a 1500 tonnes train moving on a 2.5% grade under any circumstance, and get a 1300 tonnes train up to 80 km/h at the same place.