To enable SSH on Dell Networking N-series (formerly known as Dell PowerConnect), you first have to generate the required private RSA and DSA keys. If you don't, you're met with a very secretive error message:

SSH could not be enabled.

To generate the keys, and configure and enable SSH, log on to the switch using the console cable or log on through Telnet:

Go into EXEC mode, then in CONFIG mode:

enable
configure

Generate both the RSA and DSA keys:

crypto key generate rsa
crypto key generate dsa

Now, you can enable the SSH server:

ip ssh server

Optionally: you can also change the default listen port:

ip ssh port 22

With more recent firmware versions, you are no longer able to change the SSH protocol version. It is now always 2. But if you are still running an older version, you could set the protocol version:

ip ssh protocol 2

Optionally: after enabling SSH, you can optionally disable Telnet:

ip telnet server disable

Go back to EXEC mode and write the changes to flash:

exit
copy running-config startup-config