I expect that mot of us do the same - prepare the ground and add a general fertiliser before planting. Potatoes need nitrogen initially to create the healthy top growth that will feed the tubers. A general fertiliser like Growmore (NPK 7:7:7) supplies that but the other ingredients may largely be washed away before the plants need them, to promote tuber growth. We then keep our fingers crossed on watering, rain and blight.
If you are going to feed for later, you need potato fertilisers that are high in the PK parts (the granular one our Association sells is 6:10:10), and I believe it can be add at planting or later as it is slow release. Tomato fertilisers are also high in PK, hence the sales pitches.
I never know when to water / not water my potatoes and would rather avoid creating blight conditions, so they largely get left to their own devices after I have (failed to) earth them up.