Time a charge with the charger and cable you actually want to judge. The page records the level as it climbs, so a charge that stalls, or takes twice as long as it should, is something you can see rather than suspect.
Charging speed is a comparison, never a number on its own. This page gives you the two halves that make the comparison work: an exact clock, and every percentage point along the way.
Charging runs fast to roughly 80% and then deliberately slows — the last stretch is the charger protecting the cell, not a fault. What matters is where your curve leaves the steep part. One that stalls in the middle and then picks back up is usually heat, a connector, or a cable that cannot carry the current.
A charge timed with the customer's cable and one timed with your bench supply are not comparable, and neither are two charges that began at different levels. Fix the charger, the cable and the starting percentage, and the device is the only variable left.
The load settings apply here too, and they answer what the charger alone cannot: whether the device can charge while it works. A phone that gains charge sitting idle but loses it under a heavy load is telling you the supply cannot keep up.