Yokohama's Chinatown is the best place in Japan to eat Chinese food, and the range is wider than the tourist-facing frontage might suggest. The big names on the main shopping street serve serviceable Cantonese and Shanghainese food to crowds, but a few minutes' walk into the side streets reveals smaller, more serious restaurants: Hong Kong-style teahouses doing proper dim sum from carts on weekend mornings, Sichuanese restaurants with genuine heat, and Shanghainese spots where the xiaolongbao are made fresh and the hairy crab is seasonal.
For a straightforward introduction, the large teahouses around Yamashite-cho fill up fast on Saturday and Sunday mornings, so arrive by 10am or expect a queue. Peking duck and roast meats in the window are reliable shortcuts to a good meal. In the evenings, the area around Kantei-byo (the ornate Chinese temple) has several restaurants that stay quieter than the main drag.
Budget around ¥1,500–2,500 per person for lunch; dinner at a proper restaurant is ¥3,000–5,000. The neighbourhood is perfectly walkable and you can cover a lot of ground on foot before settling on somewhere.