In all my passenger cars, I use these: https://www.ebay.ca/itm/162724139001
Since it is a one time only adjustment DC in and DC out. I use a 1 1/2amp full wave bridge rectifier on the DC in, then just hook up the AC and check the voltage at the output and connect your lights, I run my stuff at 10volts output. I use prewired 12volt led's for reference...
Marty