How to measure phase shift on AC adaptor

I’m prolly going to pick up a cheap AC adaptor that has USB built in. What’s the best way to measure phase shift.

I do have a 4 chanel scope meter is it as simple as measuring the 220v side and 9v side.

I do it using the vtshift command (undocumented) of the IoTaWatt and a special AC line cord that provides a direct line reference. I consider that to be best.

I’ve never had good results with that.