is there any chances of getting your Bitcoin or ETH wallet compromised when newbies generates new address? It is possible that a bitcoin wallet can generate a wallet that's been in use by another user?
For one new wallet get the same private key as an existing one?
Yes, it is possible. But please look at the following image to understand how many private keys are possible, and maybe you will understand how small are the chances to get the same private key as yours.
(And you could also read the topic I've quoted from, it's interesting.
--
PS. I think that the talk about 2^128 instead of 2^256 may just confuse OP.