This was what I was saying during the relocation debate. I'm not an AFC fan, and have never have been. I hate the Raiders, but they have a following since the only Super Bowl win was won by them in LA and they are gang supported (as far as gear etc...).
No one cares about the Chargers, unless they are already Charger fans, or are strictly bandwagon fans. Maybe that will be a little different now, but I don't see LA Raiders fans quitting their affiliation with the Las Vegas Raiders. Seriously, there probably can't be a much better weekend for adults than hitting casinos and watching an NFL game for a weekend experience. Raiders fans HATE the Chargers.
Rams fans from old are probably helping younger relatives to become new fans, but I don't know that for sure. After the first year in LA, the Chargers support will probably be lukewarm at best. IF the Rams put a winning product on the field this year, that timeframe will be even shorter.