Append it where?
facebook.com$293MyPasswordYouKnowIt!!123
password to gmail would be
mail.google.com$113MyPasswordYouKnowIt!!123
only annoying thing is that the passwords are long. I guess it's secure, though.
edit: see child post for clarification. I do something above for spammy sites, but for something like gmail I probably wouldn't do that.
that being said there are a lot of things you could use. you could use information in the whois, you could use the birthdate of the founder of the site, etc.
personally I believe people should use the same password for all sites and then something similar to what I described. though I use a password manager, I do always feel nervous about the implementation leaking out details
Eventually, some website you use is going to get hacked. They’ll have stored passwords as plaintext. From there, anyone who wants to hack any of your accounts knows your password format. It’s going to be obvious to them that they just need to replace the domain.
of course, you'll say, don't use a crappy password manager. and that's correct. same reason I use a separate format for sketchy sites.
for what it's worth my format isn't really as described, but it is similarly deterministic, but not visually so. the cipher is basic enough to do in your head but complicated enough that you wouldn't know from a glance
a real password example for your scrunity:
m0m2a2yiplagsosowgolredd1o2t3c!o!m2
steps:
m a i l g o o g l e d o t c o m
strategy
zip
secret
mypassword123!!
offset (publicly determinable)
0
unique: 2022
m0m2a2yiplagsosowgolredd1o2t3c!o!m2
i use a password manager so the long text generally is irrelevant. the main reason I do this is because I don't feel comfortable needing my password manager. I like being able to figure out my actual password completely independent of a phone or internet or app.
the strategy depends on how sensitive the app is (strategies include: zip, append, vowel-zip, no-vowel-zip, num-zip, all the same but with a reverse-offset). unique is usually something like when I joined, or something determinable from the site and my head.
all of this seems much more complicated than it is. once you understand you could calculate the password in your head in a couple seconds.
edit: oh, I did say append so I see why you'd think that. that's my bad. what I meant was include
Also plenty of perfectly respectable sites have been compromised in the past so your estimation about how safe the site is unfortunately doesn't help much.
I really think you'd be better off using long randomly-generated strings and keeping multiple backups of your password database. There are lots of options that don't put you in the hands of a third party. All (?) sites offer password reset facilities in case of emergency, and you could memorise your email account password so that you can always at least get into that.