If I supported another person, how does that effect the way they file their taxes? And what documentation do I need to prove the support I provided?

[bhawk]

Adult son was earning less than 4,000.  

Provided 10,000 support - rent, food, transportation

What docs, do I need to prove support?

Plus, what effect does this do to his tax return?

[Coleen3 · Accepted solution]

It does not affect it at all. As long as makes less than $4,200 (2019) and you support him, you can claim him. If he has any withholding to recover, he can file, but he must state that he is being claimed as a dependent.