550PLG-SLI problems?

January of this year I rebuilt my computer from a old 2.6c/IC7/BH5 system to a Opteron 170 system and ever since then I've had problems with DVD Burners in this system, my old Plextor 716SA randomly would lockup at 99% as would my new LG 4166B. I couldn't figure it out til tonight when I had the idea of connecting the burner to another computers power supply while still connected to this PC, the Plextor has burned about 25 DVD/CDs without so much as a stutter which leads me to believe my 550PLG-SLI is bad, but the rails all show as perfectly fine. Could it be ripple or something else causing the problem?

Anyway does anyone have any experience RMAing a supply that has perfect rails but a problem otherwise to sparkle? If they refuse to RMA it, I might be in the market for another supply and could use some suggestions on what supplies are good (I might just go all out and get a zippy provided I can find a good place that carries them).

When you say that the rails show perfectly fine, are you reading that off of the motherboard's sensors or are you using a voltmeter?

Checked with both, which is why the power supply was the last thing I suspected in troubleshooting this problem.

Perhaps the fact that my case (old liteon FS020) requires me to mount power supplies upside down isn't helping it, as it seems to run pretty hot most of the time. Although my old Antec TrueBlue 480w supply had no problems being inverted for over 2 years.