Not all USB/Serial adapers are working for console redirection. Price unfortunately is not an indicator, but I had the most luck with adapters which are also listed as suitable for serial flashing/programming - which are also available very cheap.
Also beware of the multitude of non-standard and not fully wired serial cables out there. Scrambled output might be caused by a faulty/wrong cable (or wrong console type). Nullmodem cables usually have some lines crossed and don't work with most serial consoles. A lot of cables also might have some proprietary pinout even if they have db9 connectors on both ends - Dell and HP are notorious for this, so are the various serial or rollover cables from APC, Cisco or Allied Telesis. Plug a standard serial cable in your APC UPS and it shuts down (been there, done that, got anything but a t-shirt for the downtime...)
My collection of serial- and rollover cables has grown to ~20 different kinds by now - labeling every cable after verifying with what equipment it works is essential. If in doubt, grab a multimeter and verify the alleged "serial console cable" is wired 1:1 between the connectors.
I'd say 90% of all problems with serial consoles I had were caused by the serial cable. I started marking the cables and connectors at the equipment in matching colors to keep my sanity...
That being said; the settings posted by
Phishfry are identical to those I use on 2 systems that are accessible via serial console, so the Problem is somewhere up the stack - most likely the USB/Serial adapters. Try accessing a known-working serial console with a known-working cable (e.g. on your switch) using one of these USB adapters, just to verify this works.
I mostly use
screen(1) to access serial consoles, never used putty/windows though, but if it works with another console (again, e.g. your switch) you should be fine. If you see only scrambled output, try another terminal type or check your cable (again: a "serial console cable" is not always a serial console cable...)