Join Date: Aug 2011
Location: Barcelona, London, on a plane
Programs: IB+ Gold, TK E+, Hyatt Globalist, Marriott LTP, IHG Diamond
Posts: 14,182
Always charged in local currency. The Hyatt website's conversion is just guidance.
At the hotel, if the credit card machine "helpfully" offers to let you pay in USD, that's a DCC scam to way over-charge you.
FWIW, many hotels don't even bother to make you prepay, unless you cancel or no-show.