In order to connect your 50A rig to 15A household outlet you need the 50A female to 30A male adapter like the one in your link. Connect your OEM power cord to RV outlet then plug it into adapter.
And you will also need a good 30A female to 15A male adapter. Throw that 'puck' adapter away. They are junk, overheat.
Get one like this.....
Using household outlet you can charge batteries, run fridge (level it), and sometimes can even get away with running A/C Unit.....depends on state of battery charge/how hard converter is working and items that may be on same circuit in house
ON EDIT.......
Just saw your new post.
Yes you can use that 50A twist lock to 15A adapter and a good grade extension cord to reach house outlet. At minimum 12 gauge cord
