So what doesn't work? Do any of your devices have a "Power Available" LED on the part that goes into the 12 volt socket? Does that not come on? Are you sure you are pushing them in far enough for the end to make contact?
There is a chance that you could have a corroded connection in the supply line to the sockets. That would allow you to measure 12 VDC under no load conditions but as soon as you have a load (current) the 12 volts is dropped across the corroded connection.
If you have a device plugged into one socket, do you still have 12 VDC at the other 2 sockets?
__________________
|