Need part number for a/c adapter for AX4300

AX4300 is a speed, not a model. 

Do you have the old adapter? 

Netgear doesn't sell power adapters so usually you have to buy one with matching capabilities 3rd party or from ebay. 

Netgear does not sell replacement power adapters. Any generic adapter will work, as long as it has the right volts, enough amps and a tip with the right (+/-) polarity and dimensions.

Look at the device you own. It will have a label that shows what you need.

The manual will have the information too.

Plug the details into your favourite on-line store, or visit a local shop.