I successfully got compensation on my DB sparpreis from Warsaw (PL) to Sylt (DE). Three hours late = 50% of what I had paid, in cash if I gave the original ticket at the counter.

Quote: "How do you want to prove that you really have been on a delayed train without the original ticket being punched by a conductor? "

-> the train authority knows which trains were late. If you say you were on the late train, and have a ticket for that route and day, they will assume you say the truth, so no need to run after the conducteur to get your ticket punched.