It is hard to recommend sci-fi manga since mange rarely uses the classic "superhero" tropes. I can recommend some really good sci-fi action manga and anime centered around over-the-top action, but I don't really know of anything that involves capes and secret identities.
If you are just looking for over-the-top superpowers based on advanced tech, I can recommend the Battle Angel Alita manga. It takes place in a cyberpunk world where most of the main characters are cyborgs and androids, and involves a lot of highly skilled martial artists using advanced technology to augment their fighting abilities. For example, you see stuff like plasma manipulation, nanotech-based regeneration, and electro-magnetically accelerated punches. *Warning: This series involves some very graphic violence. It is not for the young or faint of heart.*
If you are looking for traditional superhero stuff, I can recommend the webcomic
Antihero For Hire. Almost all of the stuff in there is technically based on technology, and the comic is really funny to boot.