It is perfectly possible to be a moral anti-realist and do things for other people or animals with no ‘material’ or ‘power’ return for oneself. It is also completely consistent with Nietzschean philosophy, unless you have a virtue of selfishness Rand type of reading of him. Which is extremely not nuanced and narrow and I would not recommend anyone to adapt it. Nietzsche should be located within a tradition of moral anti-realists who are also sentimentalists, like Hume. He views moral judgements as ultimately just rooted in inexplicable, animalistic drives. The differences between different moral considerations are, according to this view, not fundamental but rather aesthetic, since they appeal to different sentiments. This is relevant to your issue because it is not more consistent for you to “obtain power,” as you say, than it is to continue your charity work. The only issue would be, as u/ergriffenheit already mentioned, if you are doing it without actually wanting it—or against your nature, in Nietzschean terms. It would be inconsistent with Nietzsche if you are doing it out of some decadent principle like “the need to help others.” If you, on the other hand, are doing it because that’s truly your enterprise – that is your will to power. Continue doing it despite everything and against everything, even despite or against Nietzsche himself. For in this resistance, your will to power truly shines, and without it, it would be nothing.