Having owned several older 80's cars over the years, I've noticed that those USB chargers are kind of a hit or miss in cigarette lighters. The 12v plugs in newer cars are not meant for cigarette lighters (they will burn out if you try to use one) and seem to be of a somewhat smaller size and that is what those chargers are meant for. I have the same issue even in my Mazda which came with a cigarette lighter (now long lost). I have a 2 port charger made by Fusebox that works well in the Benz and the Mazda. I bought it at Wallgreens I think. I have several others that can only be used in my wife's Camry as they will fall out of the cigarette lighters in the Benz and Mazda with the lightest bump.

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"The MB W123 is so bulletproof, you can drive them forever. Which is a good thing as it takes that long to get anywhere."
Betsie: 1984 W123 300D (hobby, 280k miles)
Myrla: 2001 Mazda Protege 2.0 ES 5spd (daily driver, 130k miles)
The Turd: 2007 Toyota Camry (wife's car, 118k miles)