FWIW, SNAP does not support screen power control on my T510, or my L530 either.
Wonder if laptop monitors just don't have DPMS?
Testing on my T42, seems to be yes and no.
Using the stock ATI licensed SNAP with eCS 2.2B2, there is no DPMS service available on the advanced full screen thingy and the screensaver has them all blanked out. Only supports a few 4:3 resolutions too, even when plugged into a wide screen monitor, up to 1280x1024 IIRC.
Testing with a recent ArcaOS beta and ArcaNoae SNAP, the answer is sorta yes, screensaver shows all choices available, advanced full screen thingy also shows them all available but standby and Off both just seem to blank the screen and suspend does nothing. Way more resolutions available too. Wide screen resolutions seem to revert to the closest 4:3 resolution using the built in monitor, plugging into a wide screen monitor, wide screen resolutions revert to VGA (640x480). 4:3 seem to work with the monitor bitching if trying to display beyond its capabilities. The builtin monitor works right up to 2048x1536 but only displays part of the desktop with that part moving with the mouse.
One nice thing is that on the wide screen monitor, the image shows at 4:3 with black bars on either side, much better then stretched.
Edit, forgot to mention that using APM, FN+F3 turns the monitor off and Fn turns it back on