I prefer to use a high quality powerbank, not any powerbank but a high quality and I'd like to insist on this. I check all my chargers and powerbanks with an USB tester that checks voltage, current in Amperes and power in Watts, I'll post the link for this tester on Aliexpress later.
I Use an E C Technology (these can be bought on any Amazon) 22400 mAh powerbank that is absolutely stable, with the USB tester it checks 5.2 Volts (0.2 Volts won't damage any device, there's always a tolerance) and 480 mAh when powering the Topping D50, and it stays at that without fluctuations of voltage and amperage.
I also have an 10400 mAh LG I got as a present and it's also very stable, it gives almost the same readings as the EC Technology, 5.1 Volts and same power consumption, 480 mAh. The 10400 mAh LG can provide up to 8 hours of music listening. It has 4 LEDs that shows its charge level (the same as the E C Technology) and when it got to the last LED I stopped the D50, I didn't want to overdischarge the LG.
I don't know how many hours of powering the D50 can the E C Technology provide as it has 22400 mAh, maybe 16 to 20 hours. I once listened to music with the D50 powered by the E C Technology for 5 hours in a row and it still had its four leds lighted.
Powering the D50 with my Mobile phone charger that gives 5 Volts at 3 Amperes definitely changes its sound for the worse.
The E C Technology 22400 mAh powerbank cost me 24 Euros two years ago. I bought it as I was going out for camping for three days and I wanted a powerbank with enough juice to charge my mobile phone and use 3 LED lights, I haven't really used it since then but I had the precaution of every three months charge my mobile phone with it (both actually as I did the same with the LG) and then recharge the powerbank.
I've also tested a friend's 15000mAh Xiaomi powerbank and it also tested very stable.
If anybody's interested on the USB tester here's the Aliexpress link:
https://www.aliexpress.com/item/9-1...?spm=a219c.10010108.1000001.12.41333de18qtaum