feeding adult dog food to 11wk puppy

I acquired a puppy of unknown breed origin (possibly lab-X with a Shepard or husky type due to fuzzy double layered hair, no idea really). My sis found him downtown in a bigger city at 3am running on the street.

I think he was roughly 7 weeks when we got him. Now it is 7-8-10. and according to the vet he is 12 weeks-ish tomorrow.

He has been eating Purina One adult dog food since he came here. I bought some puppy chow(Iams) after he was here two weeks and he wouldn’t touch it so I mixed it with the adult food and fed to them all. They all ate it fine.

Then last week I picked up the Purina One puppy formula and he wouldn’t touch that either.

I gave up trying to feed them separately as well because I would have to starve them for 2 days (or how long?)to get them to eat when served. I have always free fed no matter how many dogs I have and they all self regulate intake very well.

I keep food at work for him because he’s been coming there all day everyday with me and hanging in a crate in the office or roaming when no customers are around.

So I took the Purina One puppy chow to work and he will eat it there but not at home.

The Purina 1 adult has 26g protein and the puppy has 28grams.

The puppy has DHA the adult doesn’t.

Otherwise the nutritional info is identical(as are the ingredient lists nearly identical)..

So, should I insist he eat puppy food or will he be okay on the adult?