if you have a fully verified coin base account that is. SO GET SPENDING. Even if you pay USD go USD to BTC to buy... it's actually cheaper that way.
How do you send USD to Coinbase/exchange/Bitpay/whatever, and what do they send to Dell -- USD, or BTC? If USD, how do they send it?
This appears to be one of those basic retarded questions of yours that could easily be answered by yourself, if you were to buy and use bitcoins then you would possibly realize how to use them. Of course, the customers pay in bitcoin, and then if Dell wants to convert them to fiat after the transaction, they have that fiat conversion option.
And that is the (non)answer that I get whenever I ask that question in this forum. I had to ask the same person three times (on another thread), before he understood the question (and answered it for only one special case).