Wasn't that just Windows 95 and 98? I think I remember XP having the Windows logo and the "It is now safe to turn off your computer" text in white.
replyNo, I recall once being surprised at seeing it in XP back in the day, on a particularly old PC that had had its OS upgraded from 9x.
replyOlder AT power supplies were entirely mechanically controlled using the power button. ATX power supplies added the ability to turn on or off via software. That screen was shown on PCs using an AT PSU because Windows couldn't shut it down itself, it had to ask the user to do it.
Evidence you’re right: this video at 1:10
reply