When is 12v dc not dc?

RobinTheBank

I recently purchased a Roberts Radio Stream 83i internet radio for use in our caravan. I purchased this model because it runs on 12v dc. I emailed Roberts because I needed a spare 12v plug and this was the reply I received ....

'Thank you for your enquiry. You may need a dc to dc convertor in order to operate the radio from a caravan. We do not stock such items and I would advise you to contact a local electrical retailer such as Maplin for advice on such an operation.

Can anybody tell me please what they are talking about? I thought dc was dc...