Desk lamp with built-in USB hub:
You have a halogen-based desk lamp with built-in four-port self-powered USB hub in its base. The USB hub is on all the time, independent of the light switch and all are powered via a multi-tap transformer.
There would be the "B" (host) socket and two "A" (peripheral) sockets on the back; with two "A" (peripheral) sockets on the front. The back sockets would be used for devices like printers and scanners, with the front sockets for "walk-up" attachment of devices like USB flash-memory keys.
Plug-ing HomePlug APs, bridges and USB adaptors with built-in power sockets. These would be connected in a similar manner to a plug-in timer or surge suppressor - plug in to wall, then plug an appliance into the socket on the HomePlug device.