[pfffr]

Some people add sugar but it is not required to achieve carmelization. Onions contain sufficient sugars to ensure this process.

[dublin]

I've found you really do need to use sweet Onions like Texas 1015s or Vidalias if you want good, quick(er) carmelized onions. Adding sugar is not the same thing at all as having the sugar grown into the onion itself!

Adding water early on in the cooking process to steam cook and soften the onions really speeds things up, too. (See Lan Lam's YouTube video on cooking carmelized onions. I use a slightly different method, but she got me on the track of adding water early, which really does help...)