Contraband is a rather inefficient Rogue card. Its best use is certainly in multiplayer. If you can add 2 ammo to a Guardian's Shotgun, that's decent. It's hardly great, though, because you're spending 4 resources and an action to do it. In terms of actions and resources, that's almost as expensive as just playing a second Shotgun! If you play it after Extra Ammunition has been played, that's better, but now we're talking about a really slow and clunky multi-card combo.
Moreover, if you draw Contraband after the Shotgun has already seen some use, then it's useless. It doesn't do anything if your friend's Shotgun is out of charges, and it's pretty lame if it only has one charge left.
Contraband doesn't go well with any Rogue cards at the moment. Note that it does not combine well with Jenny's Twin .45s. Think of it this way: if you put 5 resources into Jenny's Twin .45s, and then play Contraband, you're not coming out ahead at all. You spent 9 resources and 2 actions to get an 10 ammo on Jenny's Twin .45s, when you could have just spent 10 resources and 1 action to accomplish that without Contraband. Once you initially put in 6 or more resources into Jenny's Twin .45s, then Contraband starts to generate a little bit of profit. But at that point, you just don't need that much ammo. For instance, you could spend 8 resources and an action to play Jenny's Twin .45s, and then 4 resources and another action to play Contraband. So that's 12 resources and 2 actions for 16 ammo. If you hadn't had Contraband, you could have just put your cash into the Twin .45s directly, which would be 12 resources and 1 action for 12 ammo. So you've effectively converted 1 action into 4 ammo. But that's not actually useful, because 16 ammo is just way more than you could possibly use.
So currently, none of the Rogue cards with charges are sufficiently useful or expensive that Contraband would make any sense. That makes this card multiplayer-only, and a rather questionable pick even then. But it is totally possible that we will see some new expensive cards in the future that justify the presence of Contraband, slow and expensive as it is.
Note that this card does not work with Shrivelling, which doesn't use ammo or supply tokens.