Surprisingly, it was even easier than older models:
Dell Laptop Master Password Generator.
Copyright (C) 2011 dogbert; 2007-2010 hpgl
Short service tag should be right padded with '*' up to length 7 chars
HDD serial number is right 11 chars from real HDDSerNum left padded with '*'
Some BIOSes has left pad HDD serial number with spaces instead '*'
09.10.2011 22:42 DELL service tag: ABCDEFG-1D3B password: xvn0qEeftqyrkG52
In light of this (and this), a pack of monkeys looks sophisticated in comparison to Dell engineers. Also, please don't even bother to send me emails: you're just wasting both our time.
P.S.: DELL service tag: #NOSOUP4-3A5B password: zvd97y9h