I go to a particular "chino" for wines. Indeed the prices are much better, especially in upper-middle-range wines. What you find at Coto or Carrefour for 300 pesos, they have for 150. You're not going to find anything beyond Rutini, though. The only con is most of the time they only take cash, so be prepared.
Some years ago I lived in Palermo and had a "chino" next door. I used to go very often for my daily shopping so we had contact. He told me the Chinese supermarket owners would assemble, rent a van and drive all the way to Mendoza where they would negotiate straight with the the bodegas. The big price difference with large supermarket chains was due to the fact they didn't pay the shipment (they had the van) and they offered the bodega to pay cash, while larger chains usually paid only 30/60/90 days after receiving the merchandise. In an inflation-prone country, paying the total straight away apparently made a big difference for the bodegas.