I've had great success with generic ram in G5's of all speeds, not a single POST failure related to the ram sticks. The OP's eBay link isn't for generic ram, it's for HP branded ram.
I know, but it is a general caution. If buying generic RAM, be certain that you can refund it without a 'restocking fee'.
I have wasted money on it in the past, for late model G5s. (The 2003 and 2004 models are less problematic.) That said, I did buy PC3200, generic RAM, on eBay, from a trusted seller, and it caused a POST failure (three flashes).
I find that the 2.0GHz machines are slightly choosy, and that the 2.5/2.7GHz models are
downright aristocratic. This was otherwise solid, non-high-density RAM. One other problem that I have found with some RAM, is that the wafer width on generic memory can be off of spec by 0.5mm to 1.0mm, which makes it awfully difficult to insert in the cramped space inside a G5.
For the OP, I can't suggest more strongly that you
fill it to 8GB. The world of difference that it will give you, and the new avenues of use is truly remarkable.
You can fill a G5 with 8GB of RAM for about £50/$75!
Compare that to the near £900 that I spent when my I bought my (new) Dual G5 in 2004 (about US$1,800!! at the time), and filled it to the maximum.
If you do any graphic design, or DTP layout, or any video work of any kind,
it is a night and day difference.
Intell, and I have a disagreement on how selecting G5s are with RAM. I have had both good, and bad experiences with unbranded memory. The price difference for branded memory, with a warranty, that you can refund if you have any problems, is
to me, worth the 10% margin.
Only two months ago, I purchased 16GB of unbranded RAM for the additional G5s that I purchased (both 2.7GHz systems),
and all of it caused POST problems.
I don;t know if it is a latency, voltage, or other problem, but I suspect latency first, and voltage second. Some PC3200 RAM is
2.5VDC, and other RAM is
2.6VDC.
The MMC in the 2.7GHz systems may be far more fickle, and the 2GHz systems are certainly less forgiving than the 1.8GHz (PCI-33) systems.
The 1.6GHz and 1.8GHz PCI-33 systems use both a different Northbridge, and a different Southbridge, than the 2.GHz PCI-X/AGP systems, and I believe the Northbridge may have been changed between the 2GHz and 2.5GHz/2.7GHz models; whereas the late 2005, Quad-Core G5 systems, with PCIe use a different Southbridge than the 2.5/2.7GHz Dual-G5s (with PCIe), but I believe they retained the same Northbridge.
If this is all Greek to you, you may want to read about primary, multifunction controller ICs:
Northbridge and
Southbridge.
This is a very important topic for PPC architecture, that anyone in this forum will benefit from understanding.
I think that it's about time to start a thread on G5 upgrades...
