if your child has problem eating or refuse to eat, then you will want to give him formula to supplement what he is not enough. If he is ok and eats himself, then fresh milk will be more than enough to supplement him. At 19 months, you do not need to worry much. Milk are supplements to normal meals. Formula are higher class of supplements than fresh milk.
Baby do not eat solid so must drink milk from birth to 7 months old and optional to 1 year old to finish changing to solid food. after 1 year old, it is considered supplement.
My child rejects any food or any drink since baby. She only likes plain water. Although she rejects food, she still grow good. After 1.1 years old, she suddenly accepts milk one day and drinks herself. Later, she starts accepting some solid food and fully on solid after 6 months.
I have heard many stories baby rejects food or only eat yogurt until 3 years old and all of them still healthy. The only problem are the parents who got panicked and start sourcing specialists, hyper nutrition food,.... To tell you the truth, specialists also unable to help you because they are not god and cannot know what the baby is thinking. Babies and toddlers will changed suddenly one day so no need worry or panic.
brands are just preferences. go for price. A lot of people thought new zealand source or higher price formula are higher quality but they are wrong. There are a lot of hidden agenda from these milk manufacturers. New Zealand no longer produce quality products and have many hidden problems. Example the biggest news, You can see follow-on problems from Fontera and they had tried to hide them. Few years later, again problems came from fontera. China government also so corrupted that they promoted fontera products only.
As I have said earlier which had answered your question before and after:
"doctors must safeguard their bowl of rice. So all doctors will say powder.
If you are feeding normal meal, fresh milk is good enough.
Powder is just a supplement added. If you are kiasu and have lots of money, go for powder."