One that really gets me is the number of different sizes of DC power jack, some of which look identical but are not. For example you get 2.1mm and 2.5mm types, and although one fits the other it does not give a reliable connection.
Anyway, good luck with this product, excellent idea.
When I worked in the audio trade I had a wall hook with a whole array of flyleads. It was a question of figuring out which combination of leads would get you from one type of connector to another. If it turned out that none would.. then basically that led to another one being added to the collection.