There's been a few stories & comments about the Qi Fast charging not working except on approved chargers - defaulting to 5W rather than 10W.

I've looked for (but can not find) some graphs showing what a 5W vs 10W wireless charge over time actually looks like. I assume it's non-linear, and it's not a 2x factor at any battery %. For all the talk it's odd there's no good actual numbers though.