Are you refering to 5050SMD led's on Flexible PCB strip or you have individual ones. First you may write how you have connected or supposed to connect it as you have mentioned 20 Nos in the heading and 50 Nos in your post. In fact the flexible LED strips can be directly powered by a regulated 12 volts DC supply may be a SMPS.
Its just like a module not a strip
what i have to do is to make the bulb which had min 20 and max 50 nos
the power supply should be the same for both either i will use 20 smd's or 50 smd's as per requirement
can you suggest me the good and cheap power supply input 230v ac out put 12v dc