I've had success with the Prolific pl2303-based usb-to-serial dongle on my Powerbook configuring Cisco routers via the console port. I recently tried connecting to a Catalyst 1900 and couldn't get it to work. All I get are the strings "ATQ0H0" and "ATQ0Z0". Port is setup 9600/N/8/1 as usual. Sending a "break" causes alternate responses of ATQ0h0 and ATZ0H0.
Tried using a legacy Mac as well as a Windows PeeCee, both with built-in serial ports, both worked. I need to make sure this works on my Powerbook since it's the machine I'll be using for on-site setup.