The combinations for predicting adoption of a child by a couple are based on looking at the weakness of putrakaraka elements in the chart. The logic is simple – if there are no natural issues, adoption is the next possibility. The yogas therefore are more or less along the lines of malefic aspect on 5th (and 9th) lords/houses (thus denying children) and also on the 7th house (denying ability to procreate).
If this benefic influencing the 5th house is Jupiter, which is the naisargik putrakaraka, the influence almost guarantees birth of children as seen from various Parashari yogas. Therefore, it can mean that it is not Jupiter that influences 5th house in rule number 5 above, but it is rather Moon or Venus that are indicated here.
I would like to point out a problem with this approach. It does not consider a scenario where perfectly normal couple think about adopting a child even when they already have naturally born children. IMHO, it would be difficult to make a distinction between adopted children and naturally conceived children in such a case.