If you are working on 12V DC Power supply then you should use DB107. It's a bridge rectifier and is used to convert AC into DC but if you apply 12V DC on the AC side, still it will give you 12V DC but on the AC side you don't need to be conscious of polarity.
Read about KBP307 as well, if you are dealing with high current. Both works the same. If you need more help, let me know.