What is the DC output for your A500 AC charger? If it's the same 19V 2.15A that WyoSi reports for the AW500, you're good to go. Be sure to come back here and let WyoSi know what you find out.
I happened to be at WalMart the other day and they had an Iconia Tab A500 home charger hanging on the wall so I took a look at the specs and it puts out DC 12V 1.5A. So it appears that the A500 charger wouldn't drive the W500 tablet.
So to answer the question of this thread:
No, an A500 charger will not work for a W500 or vice versa.
Have you considered getting an inverter that plugs into the 12V DC outlet in your car and puts out 110V AC? Then, you could use your "home" charger in the car. Amazon has several in the $15 to $20 USD range that should easily be able to drive a tablet power supply.