Yes. You can still use your Philips Avent Hands-free Electric Breast Pump when it is plugged into a power source. However, please note that the battery will not charge during pumping.
Make sure that you use the USB charging cable included in the box with a 5 V/1.8 A (9 W) adapter or other power supply (power banks, USB wall sockets etc.).
Using a weaker power source may result in slower charging, and your pump may not work when plugged in.