Go out with as little armor, weapons, and miscellaneous items as possible and go looking for enemies to kill. Take their loot and then sell the loot to suppliers on the game. In Tenpenny Tower, You get a lot of ammo if you kill everyone and loot them. If you've already done this, then look for Fort Independence and kill everyone, then go to a little storage room with a missile launcher which does 30% more damage upon exploding, and you get mini-gun ammo and power armor. Enclave soldiers also carry good loot if you can kill them. Their power armor and laser rifles are rather expensive; I make, like, 500 caps off of just two Enclave soldiers, so if you do that for 10 minutes you might get 3000 caps.
2.Stealing and Scouting
Stealing from Tenpenny Towers, the Brass Lantern, Silver in Springvale and Rivet City can net lots of caps. Selling ammunition that you don't use it’s also a good way. This is just for beginners.
3.Infinite caps paradise falls
I thought I'd share the cheat. Go up to Paradise Falls and speak to the guy that first approaches you at the gate. Ask him some stuff about VIP slaves that you can capture. They're is Susan Lancaster from Tenpenny Tower, Flak from Rivet City, Red from Big Town and another is a sniper, Arkansas, I think. Once you get all three of them or one, you can go up to them and they'll ask you to free them. Select "you’re a slave deal with it." or you can do it too all 3, but if you only have one that’s fine too. After that go back to the guy who hired you to get the slaves and he'll pay you 250 caps and a slave collar each time you do it back and forth. If you already know this my bad, I just thought I'd fill you in about it even if you didn't.
4.Sydney at Underworld Ninth Circle
Sydney is now selling guns and ammo if she survives through finding the Declaration of Independence. Ask her about herself. She will cry about her dad abandoning her. Select "that's a nice gun". If you have "A note from Little Moonbeam's father", you can tell Sydney that her dad did not abandon her. She will give you her special 10mm SMG and 50 rounds of 10mm ammo. Do this as many times as you want keep it or sell it for around 250 caps depending on your barter skill.
You guys all know those pre-war books that litter the land of fallout 3. Well here is an easy way to cash in on them. Save up as many of those books as you can and then travel to the "Arlington Library" (south east section of the capital wasteland.) If you have already completed the quest for Moira Brown at the craterside supply in megaton then you probably already know this. Here there are a lot of brotherhood of steel goons and one important lady (do not kill her). She is the one you want to talk to. She pays 100 caps for each prewar book. Roughly ten times the normal value I guess.
I hope you guys liked this blog I put together it's something I took like an hour and researched a lot of stuff on it and if you don’t like it leave a post so I can revise and edit so I can make it better thank you.