Part 1: going to the past
Umbran has the advantage. A physicist going back 100 years is in position to use his primary skillset to his advantage. He could probably scoop Newton if he went back farther.
I'm a technologist, with a wide swath of other skills. Unless I happened to have all my gadgets on me (and a charger), my ability to appear wizard-like dwindles as fast as my battery capacity. After that, I'm just a madman ranting about things to come.
Assuming nothing bad happens to me, I could probably get work as a carpenter's assistant or laborer (having laborerd before, the concept isn't foreign to me).
The printing press is likely the main invention I could cook up. Maybe typewriter if I get help from a metalsmith or machinist. Otherwise, my knowledge of science to come, while advanced, isn't complete enough to "prove" anything. I know penicillin comes from mold on oranges, but I have no idea how to process it to "save" somebody to score some credibility points.
Part 2: going to the Future
As a technologist, the future is where all the cool stuff I've been waiting for is at. So for me, going there, I'll be able to adapt to what I see, based on understanding how we got to that. I'm not sure how weird it has to get before I'd be stumped, but I should hope it has to get wierder for me than most other people.
Sadly, all my mad skills will be hopelessly outdated. I can hope there's interest in history, as I could perhaps work as a technology historian or something. Though I imagine forging credentials in the 25th century is even harder for a guy from the 21st.
Part 3: bringing the past back
Consider that watching the city scenes in Bladerunner when it came out, is akin to bringing one of those current day primitives to New York City. A lot of hustle, bustle, and seeing things you've never seen before.
Nobody died from that. And if you have somebody explaining it all to you, at least so you know what its called, can make the transition easier.