wifi shield external power problems


I have a working sketch running on Arduino Uno+Wifi shield, this sketch measure electrical power using emonlib and current sensor.

I send consume values on thingspeak cloud through wifi shield connected at my home wifi.

Until now I had always connect my Arduino directly with pc usb cable, and it works.

Now I try to plug from external power source using same usb cable but with my smartphone power supply (5v output like pc usb) .

With this connection I not see the green link led on wifi shield and data is not sent. I don't know what happens becouse I can't see serial monitor.

I try a direct power supply too with same results, this is the power supply model :

Manufacturer & model: Ideal Power Ltd. 77DE-06-09

Input: 230-240V AC 50Hz

Output: 9V AC

Output: 666mA

Power: 10W

2.1mm barrel jack

You need 9V DC, not AC.

What is the current rating on the smartphone charger? I use a 1A version and it works ok.

my charger is 0.8 A . I try now using another charger, 1A this time, and all works fine.
thank you !!