PLEX is the company that designs everything for Super Sentai from suits to mecha to weapons. The company approximately started about eight years ago, they grew from the Popy company that took care of that task since the beginning of the Super Sentai in 1975. Popy is the first company to manufacture the Super Sentai toys and products and also designing the Super Sentai artifacts. Nowadays, Bandai is the company makes the toys for Power Rangers and Super Sentai for all over the world. Plex also has designed the Titanium Ranger's weapons and rumored to had designed all the Bandai America toys. I say rumor because it has not be confirmed. Plex also manufactures some things, mostly keychains and cell phone chain figures.
This is how the chain of command works for Power Rangers. First of all, Disney, Toei and Bandai own part of Power Rangers. It is shot and made by Village Roadshow in New Zealand, original footage from Japan by Toei, distributed and owned by Disney, Bandai America produces and distributes the toys, Plex designs the props and toys, and Rainbow Productions manufactured the monster suits.
Visit the official Plex website.