Express consoles began shipping with a new power supply on 10/8/2002.
The obvious difference between this power supply and the original power supply is the connector from power supply to console. The two supplies are physically different enough, that they are incompatible.
Both power supplies have since been replaced with newer versions that add a ground pin to the wall plug.
When ordering a replacement power supply, make sure to check the connector on the console or the old power supply so you can get the correct one.
See Also: Pinouts for Express Power Supplies