By Deepa Seetharaman SAN FRANCISCO (Reuters) – Startup Stripe and Chinas Alipay have struck a deal to allow Chinese buyers to pay for purchases on the U.S. service, in a rare agreement between a Western payments service and the Alibaba affiliate. Alipay, once part of Chinese e-commerce giant Alibaba before it was split off, handles about half of all online transactions in China. Stripe said the deal will let its own customers more easily handle purchases from the worlds second largest economy. Stripe, which is often compared to Ebay Incs PayPal, said few of the credit card brands it supports are used in China.