If you capture other's planet, you will get some hardware. You can reserve engineer it and try to understand "What is it?" and "How is it working?".

How can it work on the game? When you capture a planet, you have a change (10-50%) to get building or planet improvement (used on this planet before your invasion) which you don't know. After a few turns delay, you will get some knowledge (3-20%) of the technology, which was used in this building or improvement. You can improve your understanding of this technology and reduce research time to 50% maximum.

Also, you can get some knowledge about terraforming (if the planet was terraformed) (3-10% change) or empire improvements (0-5%), maximum 50%

You should see /#/endless-space/forum/29-archives/thread/13493-suggestion-ship-salvage-and-technology

I read it, it about ships and have some differences from this idea.

Your idea makes sense. If you conquer a system of a race that has higher levels of tech than you (and assuming said system is built up enough) you should be able to get some kind of benefit from it aside from just what is already on it. I wouldn't mind being able to maybe destroy some of the advancements on these system for the chance to get more tech without researching it.

If anything, it should give a certain % reduction to the research cost of said item's technology.