1998 Plymouth Voyager charging

Hi I have a 1998 plymouth grand voyager the van started acting up I pulled into a gasstation shut it off and went to start it back up and all I got was click, click, click. So I got a jump from a friend of mine drove it home about 10 miles or so got home shut it off. Started it back up fine about 3 times the last time I took off the neg cable off the battery it died right away sounds like alternator so I replased it. Battery still won't start it so I charged it enough to make it start. Battery light still on so I take wile it's still running to the local auto parts store they told me by checking the battery is bad so I buy a battery starts every time but the battery light is still on. They checked the charging system and told me it's only putting out 12 amps not 14 like it should they then told me the regulator was bad which was in the computer. Can I use one from another van the same evrything or does it have to be a new one and be flashed over. What should I do cheeply as possable than you please let me know