Many years ago there was a price difference between and 1N4001 and 1N4007. But due to mass production, the price gap was closing. If I go to my local spare part store I can still get 1N4004 and they are mostly old stocks. But if I buy mail-order I can only get 1N4007 like here:
http://www.escol.com.my/Transistors.html#Diode,%20rectifier,%20bridge1N5408 was also the same. Many years ago I saw people using 1N5401 but today most people just buy 1N5408. Did you open up the AC adaptor and check what rectifier they used inside ?
robosang WROTE:why are some still using 1N4001 or lower number than 7 since 1N4007 have better specification in all aspect?
I dont know
Maybe some designers dont want to over-spec too much! If you have an output of DC 12V with the secondary of the transformer at 9V ac, 1N4001 can easily do a good job, then why bother with a 1000V diode.....Or maybe if you buy 1N4001 in bulk, say 100K pieces, then may be there is a difference in price than if you buy the same amount of 1N4007.
Allen