As I looked for further information about Kecap Manis, it seems that this is very similar but the Indonesian version has various spices in addition to the sugars and soy sauce.
What I have is Healthy Boy brand Sweet Soy and as I read the fine print, this is made using what it calls the "modern method." It's only various sugars, water and soy sauce. The lettering on the bottle is Chinese and Thai and in roman alphabet "Yan Wal Yun," which is the biggest sauce company in Thailand. Since it was a friend visiting from Bangkok who suggested it, I'm guessing it's a staple of Bangkok kitchens. She also helped me pick out a variety of curry pastes. As she said, "You don't think we come home after work and mix the spices from scratch!"
Thanx for your question because now I know for my purposes to stick to the Thai (unseasoned) sweet soy because I use it without expecting it to add more than sweetness and soy umami. Hmmph. Ya learn somethin' new every day.
That's why I love these challenges, and cheftalk! Great hearing from people from so many different places. We have Healthy Boy brand here, I'll look for it.