Is it a cold boot, or do you see little white boxes on the bottom part of the screen after the XP logo? The little white boxes filling up (not scrolling), means hibernation.
As for standby, it needs continuous power. Continuous! So if you put it in standby, then the DSATX cuts power after so many seconds, then it loses all of it's info stored in RAM (which if you know is volatile memory meaning no power = no storage). I don't have a DSATX but the principle is the same for all PSU's and shutdown controllers. Check the manual and find out what the soft off/hard off defaults are. If you see something like 5s/45s, then after you pull the key, nothing happens for 5 seconds. Then it goes into standby. 45s later if nobody has rewakened it, it essentially rips the plug from the wall and no power at all to your computer.
So you can set that to something like soft off after so many seconds and never hardoff, then basically it will go into standby and keep the computer in a low power on state (S3) until you or the DSATX pushes the on button again, and it springs to life. Now, if you don't push your button/start your car for a few days, then you will have a dead battery more than likely, because this will never shut off the computer by pulling the plug. Always constant discharge.