Does new baby impact child support from ex?

My friend just have a new baby, she is receiveing child support for her old son from her ex-hu*****and. She works too. She wonders if it will raise the child support for her old son from her ex since she has to raise the new born that drops her income.

If so, how much difference? is it big enough that deserves her to request child support modification?

On the other side, if ex-hu*****and has a new baby, can he drop the support to her old son?

Thanks!