(*6W* refers to the total power throughput, not what arrives at the battery.) In some Samsung phones, the total charging power throughput gets capped at 6 watts while the screen is turned on. There is no technical reason for that limitation. If it actually were to prevent overheating, it would not limit to 6W so in a cold environment. I also have noticed that the limitation does **not** occur shortly after booting, which means that apparently, the operating system deliberately sends a signal to the charging circuitry to limit the wattage to 6W. I have not tested it with newer Samsung phones yet (S9, Note 9, S10, Note 10), but I think they already don't have that limitation anymore. The correct way to handle charging while the device is on is the *spare current method*. The method laptops have been using for decades, and some smartphones actually use. The *spare current method* keeps charging the battery at an unaffected speed while the device is used, by using **additional** current (if a power supply can deliver it) to power the components of the device. If the power supply is exhausted (at maximum current), then the power demanded by the device components should be subtracted from that current **without reducing the total power throughput.**