I've designed this holder to fit our Braun Oral-B Pro 600 toothbrush chargers. It is press-fit on a dual power plug adaptor (1x Schuko to 2x Euro) and the entire contraption is nicely held in place by the wall socket. The chargers are attached to the holder using double sticky tape.

I purchases the power plug adaptor for just 2€ at a local convenience store - sorry no part numbers available but it is 41 x 41 mm in dimensions.