Arduino + dfPlayer + CC1101 only works when connected to PC or batterybank

I have an Arduino Uno clone, a dfPlayer module and a CC1101 D-SUN module. The CC1101 module looks like this:

When I connect the Arduino with my PC via USB,everything works fine.
When I connect it with any phone charger, something goes wrong. (The orange LED of the dfPlayer caught my eye btw because it doesn't turn off.)

I'm pretty sure I correctly wired everything together. I have also double checked that everything is actually connected as expected using a miltimeter. (So it shouldn't be a faulty wire or breadboard.)

Wireing between CC1101 module and Arduino Uno :

GDO0 -> 6
MISO -> 12
MOSI -> 11

CSN -> 10
GDO2 -> -
SCK -> 13
VCC -> 3.3v

Wireing between dfPlayer module and Arduino:

VCC -> 3.3v
GND -> GND (Yes, I connected both GND pins of the dfPlayer to the Arduino's GND)
RX -> 1k resistor -> 8
TX -> 9

I'm not using Serial in my sketch. But just in case I have tried bridging ther Arduino's TX and RX. It made no difference though.

So yeah the usual issues for "Arduino only works on PC" don't appear to be the problem.
I mean missing ground connection and a Serial.begin call.

I'm running out of ideas. I ripped everythong appart multiple times replaced the Arduino, wires and breadboard with brand new ones multiple times and even continuity tested the connections. I just don't understand what is wrong here.

My sketch can be seen here: Long-Range-Arduino-Doorbell/ArduinoDoorbellReceiver.ino at master · T-vK/Long-Range-Arduino-Doorbell · GitHub

The DEBUG variable is commented out and I have verified that there is no Serial output when I do so. (In case you were thinking another library might define DEBUG.)

I just tested it with a battery bank and to my surprise the Arduino does work correctly then.
Still, it's not working no matter what phone charger I use.
Something else that just seems weird to me is the orange LED on the dfPlayer module:

Arduino connected with PC: Orange LED is off
Arduino connected to powerbank: Orange LED lights very dimly
Arduino connected to phone charger: Orange LED is on

A phone charger may be too weak for your hardware.

The same may apply to your "battery bank" - what's that?

A power bank may turn off if not loaded with a minimum current.

My phone chargers all have at least 2000mA and my project works fi e on a 500mA USB 2.0 port

Measure the exact operating voltage provided by your various PSU when the problem manifests. Use a scope to find unwanted distortions. Add capacitors to each module's power connectors.