Truly universal DC adaptor

I'd like a single DC adaptor that works with all of my many electronic devices: phone, eReader, speakers, MP3 player, camera, AM radio, and so on. I've bought 3 or 4 of them over the years, and though all come with a variety of output voltage and plugs, they never seem to work with 90% of the devices I need them for. Is there a truly universal DC adaptor available anywhere?