Caps (bottle caps) are the currency of the Mojave, and the console lets you hand yourself as many as you want in a second. The trick is that caps are just another inventory item with a base ID — 000000F — so you add them with the same player.additem command you'd use for any other item.
The caps command
Open the console with the tilde key ~ (see how to open the console), then enter:
That adds 1,000 caps. Change the last number to add any amount — the syntax is player.additem <item id> <amount>. For 10,000 caps:
Why the ID is 000000F
000000F is the base-game form ID for "Caps" (the leading zeros can be dropped, so 0000000F and F work too). Because it ships with the base game, the ID always starts with 00 and never changes between playthroughs — unlike DLC items, whose codes start with a variable two-digit prefix (see how to find your DLC number).
Removing caps
To take caps away instead, use player.removeitem the same way:
Spawn other items too
The same command spawns anything in the game. Browse every base ID on the item codes list, or see the full guide to spawning items and weapons.