I'm sorry, but I do not know what is "ASCII-armoured" password file. WinSCP uses the same format of the private key the puttygen generates. What is your SSH server? In general the server just want the public key line you see in puttygen window.
Could we get a question about
using keys under WinSCP in the FAQ?
My server only allows key-based authentication (no interactive passwords)
I have not been able to get it to work with puttygen.
It seems like puttygen only saves ASCII-armoured password files, and WinSCP/sshd
want non-armoured versions.