I've just downloaded and installed the XP DDK. It does not contain PWRTEST.EXE. I can even tell you why: the Power IRPs needed for most of what PWRTEST does don't actually exist pre-Vista. In the past, I've had to write a device driver that poked around in undocumented structures to implement some of what it does.

That said: the go-to-sleep-and-wake-up-again functionality should work fine on XP; it's just that it doesn't appear to be in a canned utility in the DDK.