SAN FRANCISCO/NEW DELHI/SEOUL April 18 (Reuters) - Tesla’s long-awaited plans for an affordable car include a U.S-made, stripped-down version of its best-selling electric SUV, the Model Y, but the production launch has been delayed, three sources with knowledge of the matter told Reuters. Tesla (TSLA.O) has promised affordable vehicles beginning in the first half of the year, providing a potential boost to flagging sales. Global production of the lower-cost Model Y, internally codenamed E41, is expected to begin in the United States, the sources said. That would occur at least a few months later than outlined in Tesla’s public plan, they added, offering a range of revised targets from the third quarter to early next year.