Alright. Today I went out and bought an Antec 380W Neo HE Power Supply. Before I installed it I checked my voltage levels in the BIOS monitor. Based on what I've been reading, the reported dips in the 12V stream down to as low as 10.8 looked fishy to me. I guess that would explain the behaviour, no?
Unfortunately my new power supply didn't work as that series apparently doesn't work its additional 12V line isn't plugged in, and my motherboard has no room for it (the 20 pin connector is enough). I checked a forum where I found that Antec has responded to numerous tech calls with this diagnosis.
So when I get the chance I'll exchange it for something without that issue. In the meantime I opened my old PSU and blew about three tons of dust out of it. Right now, it's running as follows:
+3.3 = 3.25
+5.00 = fluctuating between 4.93 and 4.96
+12.00 (which is the processor right? and hence where a hard lock might occur if too low?) = 13.01
How do these seem?