I have a write-up that I'm working on to hopefully clarify a bunch of this, but it is slow going and unfortunately there are a bunch of edge cases and exceptions that don't make talking about this easy.

The bottom line is that if you use a Type A charger, regardless of what's on the label, on 90+% of the chargers you might use, the Switch will only draw 5V 1.5A or 7.5 watts.

7.5 watts is right at the threshold where in full brightness, full volume, wifi on, I can reliably get the Switch to drop about 1% every 11 or so minutes. Under the same circumstances, I can also get the battery to hold the line. It is scene dependent. If you drop the brightness and other factors, you increase the likelihood of either holding the line or even slowly charging while playing. This is where the confusion comes in-many people reporting on their Type A chargers are testing it at all kinds of settings, and whether the charger will charge or not is not binary. There aren't "good" or "bad" Type A chargers, they are all largely the same (delivering 7.5 watts) and the variation in results is the result of a spectrum dependent on the gaming scenario.

Anyway, if you want to reliably charge the Switch while playing, it is kinda simple--pick a charger that uses a USB C-C cable. If it's C-C on both ends, worst case scenario, you are sending 5V 2A. If your charger has USB PD, you might send more, but you'll at the very least send 10 watts.

Use a Type A charger if that's what you have; it will work, not harm your Switch, and in most cases, will charge your Switch slowly. But if you're looking to spend money on a new charger, there's no reason not to choose Type C.