There are better quality foods out there than Prism - so in the longer term you may wish to switch to something better. It doesn't have to be something with "puppy" on the label though - many adult foods are equally or better suited to pups. Or put a different way, what is actually IN the food and in what quantities matters a heck of a lot more than the label. Sometimes the label is the singular difference

And sometimes the adult food is better. In short, forget "puppy" and "adult" labels and look at the part that matters (the content).
Whatever you choose to switch to though, I would not recommend doing so hastily. Even if your pup had come home with a total junk food I'd suggest sticking with it for the first week,
then gradually changing over to whatever better food you've selected. The reason for that is that already rehoming is an amazingly stressful process for puppies (and that on top of the battering of vaccinations, deworming and so forth they're already enduring). A change in food right away is just another stress they don't need, and in some cases will prove a stress too far - and you end with upset tummies and diarrhoea, which is no fun for anyone (least of all the puppy). A week on a less-than-stellar food will do far less harm.
In short, stick with what you've got for a week or so. Take that time to decide on what you'd like to feed instead. And then swap over
gradually to the new food.