The differences between N + らしい and N + っぽい ?

っぽい tends to be blame i suppose.例えば、かれはこどもっぽい。(in this case being childish isnt good.)
あぶらっぽいたべものをたべないようにしています。(I am trying not to eat oily food.) As you can see (oily) isnt good right? 
かれはわすれっぽいてす。
He forgets alot. ( Which is not good )

らしい is used when you say something is look alike or seem to be.For example,
かのじょうはおんならしいてす。
She seems to be feminine.
In this case, She is feminine and  it is suitable because she is a girl.
But you can only use this to somthing which has same properties.
かれはおんならしいです。🙅‍♂️❌ This is totally wrong.
You cant use らしい like that to say
He seems to be feminine. Instead, you can use みたい. For example,
かれはおんなみたいです。
He seems to be feminine.(He looks like a girl.)
Hope this helps.