If you're unsure about a bit of grammar, see what happens when you look at it in a much easier sentence. I'll demonstrate this with an example.
A student asked me this question:
Should we write "Companies A and B saw waste output fall" or "Companies A and B saw waste output fell"?
I told the student to consider an easier example:
Do we say "I saw him go" or "I saw him went"?
Hopefully the easy example above makes the grammar point much clearer. "Companies A and B saw waste output fall" and "I saw him go" are of course correct.