[q] And while I call it a ripple you call it a drop.. big woop..[/q]
Well, perhaps I'm nitpicking a bit, but since the current ATX12V Power Supply Design Guide, ver. 2.2, has two vastly different specifications for the voltage regulation and ripple/noise, ripple and voltage drop are NOT the same thing and blending the two together is just wrong.
You first gave the spec of 5%....you said the voltage drop was within the ATX spec of 5%...and that's NOT the ripple spec. So calling it ripple is mixing two different specifications....which, to me, shows a bit of a lack of understanding in what you are seeing or referring to.
From the aforementioned specification guide:
3.2.1. DC Voltage Regulation (Found on page 11 of the guide...link below)
The DC output voltages shall remain within the regulation ranges shown in Table 2 when
measured at the load end of the output connectors under all line, load, and environmental
conditions. The voltage regulation limits shall be maintained under continuous operation
for any steady state temperature and operating conditions specified in Section 5.
DC Output Voltage Regulation
Output Range Min. Nom. Max.
+12V1DC
±5%
+11.40
+12.00
+12.60
Volts
+12V2DC
±5%
+11.40
+12.00
+12.60
Volts
+5VDC
±5%
+4.75
+5.00
+5.25
Volts
+3.3VDC
±5%
+3.14
+3.30
+3.47
3.2.6. Output Ripple/Noise
The output ripple/noise requirements listed in Table 11. should be met throughout the load
ranges specified in Section 3.2.3 and under all input voltage conditions as specified in
Section 3.1.
Ripple and noise are defined as periodic or random signals over a frequency band of 10 Hz
to 20
MHz. Measurements shall be made with an oscilloscope with 20
MHz bandwidth.
Outputs should be bypassed at the connector with a 0.1 µF ceramic disk capacitor and a
10 µF electrolytic capacitor to simulate system loading. See Figure.
Table 12. DC Output Noise/Ripple
Output
Max. Ripple & Noise
(mV)
+12 V1DC 120
+12 V2DC 120
+5 VDC 50
+3.3 VDC 50
-12 VDC 120
+5 VSB 50
Please note the REQUIREMENT for measuring ripple.....you HAVE to use an oscilloscope to measure it.....a DMM will NOT measure ripple.
Because of this, I wonder if you truly understand the difference between the two measurements, and wonder, too, if your power supply tests are valid. If you do not understand the basic design specifications, but instead banter about specs and attribute one spec for another, what else are you not understanding in your testing?