Is there any way that you can get infinite caps in fallout 3 on the PC without cheating

"yes."
Well that person left an extremely helpful answer there.
There is a way that involves using the vendor glitch, you may or may not consider this actual "cheating".


Look for a weapon or armor vendor, as this involves the armor/weapon condition affecting the price the NPC is selling the item for.


Choose any item he has two of. Normally he'll have a more expensive one that is in better condition and a cheaper one that is nearly broken. Buy the cheapest one, the nearly broken one, and then sell it back to him. Buy the cheapest one again and it should have repaired itself and now sells for full price (sometimes you have to repeat the buying the cheapest selling it back a few times before the item in your inventory updates to full repair and you can get the highest money for that item by selling it back to him).


It's also a way to get a free repair on any item you have as long as the vendor at least has one of that item. If he has one and you have one you can sell him yours and do the buy cheapest sell glitch to get all of the vendors money. Then you may buy anything you like in his inventory and not break the bank!


You may consider it cheating to use this glitch, and then you may just decide to put your points in barter when leveling up to get better deals without the glitch.


Hope this helped better than the Yes there is one answer :/