To get SH404SEF working with System Cache plugin, make sure the plugin is LAST in the order settings.
If random å foreign characters appear when cache turned on or when you refresh the page a couple of times.
1) clean the cache
2) try to make sure the random characters aren't in the jos_content table. Using --default-character-set=latin1 should fix this.
3) run the Phoca tool on the database to change the collation to ensure the table collations are set to UFT8
4) add to line below to the local php.ini file (this is the main fix) :
default_charset = "utf-8"
5) clean cache, hey presto! 2 refreshes and should be fixed.
NOTE: phpinfo() might say the master setting is UTF8, ignore this, forcing the local to UTF8 gets rid of the strange A characters.