This takes place in the idealization/love-bombing stage which can last from a few weeks to several years. They get their narcissistic supply when you admire and appreciate their generosity.
The narc doesn’t think, “I want to make them happy because they’re so special to me”… the sad reality is, “I do these things so they will acknowledge just how amazing and wonderful I am.” This also enables the narcissist to groom you for the coming abuse.
It also happens during devaluation when the narc begins to suspect you’re pulling away before THEY are ready to discard you. They will reel you right back in with intermittent reinforcement so you believe your soulmate from the beginning of the relationship is back… while still keeping on your toes because you don’t want to lose them again.
Finally, altruistic narcissists give freely and generously in order to feel superior to those receiving and all who witness their acts of “generosity”. Again, there is absolutely nothing good-natured or pure-hearted about the narc’s actions and intentions. It’s all for the “coffee” (supply) and nothing to do with the “coffee maker” (source).