[2020] How do you cap farm!?

There are numerous ways to increase your caps. Make sure to get the hard bargain perk card to rank 3 and then sell things to the in-game vendors each day to get 1400 caps a day. The things I like to sell which I don't use are meat, excess chems, weapons, armour, veggies, etc. Hard bargain helps you sell for more and you can even pop a grape mentat to get better selling prices. Once you get a lot of items and plans, you can sell them to other players via vendors (which are disabled at the moment unfortunately) and that'll help you get more caps. There are also events like the Scorchbeast queen fight and others which give you caps as a reward. Also, be sure to equip travel agent whenever you fast travel, to save even more caps.

Hope this helps mate :)