"Couldn't agree a key exchange algorithm" error with SSH/SCP connectins to ESXi or vCenter Server Appliance

Products

• VMware vSphere ESXi

Issue/Introduction

Symptoms:
SSH or WinSCP connection to ESXi host or vCenter Server Appliance fails a message similar to:
Couldn't agree a key exchange algorithm (available: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521, diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,)

Environment

VMware vSphere 6.7.x
VMware vSphere 7.0.x

Cause

The Couldn't agree a key exchange algorithm is expected behavior with older versions of PuTTy or WinSCP.

Resolution

To resolve this issue, upgrade PuTTy or WinSCP to the latest version via the below links.
http://www.putty.org/.
https://winscp.net/eng/download.php 

Try using PuTTy or WinSCP from a different computer/laptop if applicable.

If you still get the error while trying to connect to vCenter even after upgrading WinSCP or from a different computer/laptop follow KB Error when uploading files to vCenter Server Appliance using WinSCP (2107727)