Your wife is the person whom the courts will hold legally responsible to provide for the child. Your income is just that -- your income. While with re-marriages it usually ends up that the new spouse ends up contributing to the support payment in the long run they are not legally responsible for it.
The ex's petition will lead to a "discovery investigation" where your wife and the ex will both provide their financial information to the courts and the court will re-examine the case to see if an increase is warranted. However, unless there has been a significant change of circumstance (ie your wife's finances) it is unlikely that an increase will be ordered.
