So I have been testing the Xiaomi 20000mAh gen 2 powerbank with the switch. And it seems like it cannot charge the switch efficiently when playing Zelda. So I drained the Switch's battery to 75% and plugged in the xiaomi powerbank, after an hour of playing Zelda, the battery still reads 75%. So although it is not the optimal solution it can still provide enough power to keep it going.
I have already verified that the powerbank is an authentic xiaomi product. I have also tested with a few different cables. I even bought a cable from Apple to test. All yield the same result.
I have a volt/amp meter which I checked with and the switch is only drawing about 7W of power from the powerbank. IIRC i read somewhere that it needs at least 8W to charge and play at the same time.
I'm not really that disappointed given that I got it super cheap with the shopee deal.
I'll probably be hunting for another powerbank, if anyone found one that can charge the switch to 100% while playing zelda do let me know. Thanks.