When a battery is charging, does it also get consumed simultaneously? Like, is the device still powered from from the battery instead of the power adapter, though it is also charging?
Different adapters are different wattages. It's definitely possible, for both laptops and phones, to have an adapter that outputs less than the device is using. So you can be both plugged in and drain your battery especially if doing something intensive like running a high frame rate game. Some of the older macbooks, if you remove the battery, will actually refuse to run at full speed and clock down their processors.
I'm not sure what kind of adapter is on which kind of Macs, but if you're asking because you want to use a larger brick, then it might be just fine. Let me tell you a little story:
I have a 13" MBP since 2008 (or 2009?) on which I replaced the power brick at two times, just a few weeks after the warranty was gone. Every time with another Apple charger, the same model, despite the fact that rating on their store was one star. All this time, the charger was so hot that i could barely touch it.
I was somehow disparate because it was ridiculous to take the charger as a consumable that needs to be replaced every year, so I started to do some research and I found that I could just use a larger charger (from the 15" model). I bought one back in 2013 and it runs ever since, with no issue at all. The brick is also barely warm, so that's nice :)
If you want to use a smaller charger, it will also work. Somehow. It will wear out the charger very quickly and it will take a lot of time to charge the battery.
