Thanks for the welcome!
I have opened it and it is just 7805, 7905, 7815 and an old ua723 so it isn't complicated at all. Some will be be replaced to LM317 so the voltage outputs will be adjustable and closer to +-15V. It isn't a challange, it is just a couple of hours work.
I will probably not add more features, even though it would be fun. Most likely i will make a similar but more modern for future use and if somebody like to get a kit to start with. It could be fun.
B-O