Düsseldorf School is less a genre and more a very early movement in the history of electronic music. After World War II in the German town of Düsseldorf many artists such as Kraftwerk, La Düsseldorf, Neu!, and DAF became the first to create electronic music in a non-experimental way that was much more pop-oriented and accessible than what the Berlin School artists were doing. (Kraftwerk's Florian Schneider has stated that although they were aware of what Berlin School artists like Tangerine Dream were doing, there was little interchange between the two groups, in part due to the political difficulties involved in traveling to West Berlin during that era.)
Düsseldorf School goes back as far as 1970 and developed further as far as 1986. Düsseldorf was the mecca of early electronic music and led to many genres such as krautrock, synth-pop, and space music. It also paved the way for EBM (electric body music), techno, and electro. It was largely a punk-based movement with an 'anything goes' mentality. Many artists were seeing how cheaper Japanese synths could be used in genres of their time like rock and even creating entire musical pieces comprised entirely of electronic instruments like drum machines and synthesizers. While this bit of history is largely forgotten outside of Germany it is crucial in understanding popular electronic music and how it developed. Kraftwerk have been cited as the influence of countless artists of the 80s that created major electronic music genres that still stand today. Rudi Esch is largely the one who has captured this movement firsthand with his book "Electri_City: The Dusseldorf School of Electronic Music" which has many interviews and antecedents about Düsseldorf during this formative time.