Aren't you using some old version of PuTTY? Because I cannot understand how come that you can connect with WinSCP, but not with PuTTY.

Anyway, even in WinSCP you can configure preference of KEX algorithms.
https://winscp.net/eng/docs/ui_login_kex
WinSCP will then propagate that settings to PuTTY.

On one (not both) of my Windows 7 Pro computers, when I try to start a PuTTY session from within WinSCP, I get the error: "Disconnected: Server protocol violation: unexpected SSH2_MSG_UNIMPLEMENTED packet". On that same computer, I used to get the same message using standalone PuTTY, but fixed it using the solution I found at https://www.youtube.com/watch?v=tywQX5wTKvQ, which involves changing the priority of the KEX algorithms so that "Diffie-Hellman group 14" is at the top and "Diffie-Hellman group exchange" is demoted to third place. But this solution apparently isn't available for PuTTY invoked from WinSCP. Is there a fix for this that works for WinSCP?

~ Thanks in advance, Ken