Powering servo problems

Hello, strange problem happens when trying to power servo motor (I'm dumb or I'm missing something). I've made 5V power out of usb cable, so i can plug it in PC or 5V AC-DC adapter (phone charger). If im trying to power with adapter, my servo doesn't work, it twitches a bit when plugging in. but with same cable, if I power with PC usb, it works fine. What am I missing here? 3 different adapters tried: 5V 550mA; 5V 1A; 5V 2A.

P.S. Tried with 3 different servos; With Uno and Nano

Are connecting the external power supply (USB cable?) ground, servo ground and Arduino ground all together? You should.

groundFungus:
Are connecting the external power supply (USB cable?) ground, servo ground and Arduino ground all together? You should.

Yees, thank you, I just needed to connect arduino and power cable GND together.

Check your servo stall current. The power supply needs to be able to handle that, and it can be well over 2 Amperes.