The problem here is that you have to follow both the logic and implications of what you propose. You want to go in to the past with your knowledge and "invent" something presumably prior to what we non time travelers believe to be the date of its invention according to our recorded history. So what happens when yet another time traveler goes even farther into the past and "invents" it? Every speculator/time traveler would be hop-scotching farther and farther into the past to try to invent the gadget before the other guy invents it.
You now have two tough problems.
Problem 1: If time travelers can go into the past to an arbitary date and "invent" something that already exists in their "present", where the heck did the gadget actually come from and who invented it? It seems to have always existed, was never actually invented, came from no where and therefore no one would actually have any reason to invent it at all. It already exists. Taken to its logical conclusion, everything that can possibly be invented already exists in all time frames. Time travelers have forever to travel to the past and take along their technology with them. Forever is a long time, secrets can't be kept forever, mistakes happen and technological secrets leak out. Eventually even the time travel gadget technology leaks out into the past. Everyone would have access to a time machine going all the way back to whenever humanity arises on the planet. And "humanity arises" would take on a very new meaning because people from the far distant future would be there in the past. There would be no beginning of humanity as we would define the situation. No one would have any doubts about time travel being possible and no one would even think about inventing time machines. They already exist and have existed for as far back in history as they can imagine. Thinking about inventing things wouldn't even occur to such a society...which brings into question the reason they took technology into the past in the first place. According to their history it was already there and there would be no reason to keep anything about there technology a secret from anyone or any time frame. They've been there and done that already.
Problem 2: The second problem is that there would be no money to be made because there would be no markets in which to invest. Markets depend on uncertainty. People speculate money on the uncertainty. There's no uncertainty here. There's nothing on which to speculate if the technology already exists. It would be akin to marketing snow to Eskimos.
If time travel is what you envision it to be then it has not and never will be invented. The evidence is that the world of perfect technology does not exist here. As I said, we would have forever (from today on to the infinite future and back to the infinite past) for folks to meddle with the past and untimately have their technology appear at all times and places. We don't see that anywhere.
