PowerMac G4 Sawtooth IDE>SATA adapter for HDD>SSD conversion.

This suggestion sidesteps the issue that you're describing, but would you prefer to install a SATA controller PCI card in your G4 instead? This no-name card is described by the seller as being compatible with most G4 models, including your Sawtooth. Buyer feedback confirms that it is. Sonnet and FirmTek were two Mac-compatible brands that marketed SATA PCI controller cards for older Macs, before PCIe replaced the interface. Those older cards are now discontinued.

Contradicting my own speculation about OS 9's compatibility issues with SATA technology, I came across this discussion topic in which I participated over 2 years ago. In it, the author ended up buying a FirmTek "SeriTek/1S2" SATA PCI controller card for his Quicksilver G4. It was compatible with both OS 10.4 and OS 9.2.2, so with a card that was designed/marketed specifically for Macs, a SATA upgrade was/is possible. The card that I linked on ebay is probably a flashed, PC SATA card with a Mac-friendly controller chip. A smaller ROM chip capacity may be responsible for omission of OS 9.x support when it was flashed. If you could find a used SeriTek card at a reasonable price, your goal would be accomplished.

What is the StarTech model, this one?

https://www.startech.com/en-eu/hdd/ide2sat2

Here's some others, all should work...

https://www.newegg.com/p/17Z-00W6-00034

https://www.amazon.com/SinLoon-Female-Adapter-Computer-Interface/dp/B07TPBC34F?source=ps-sl-shoppingads-lpcontext&ref_=fplfs&psc=1&smid=A69X5KMJHM850

Are the IDE jumpers set correctly?

Last but not least...

• Power Macs earlier than the 2002 Quicksilver models do not have built-in support for IDE hard drives with capacities over 128 GB. Without a third-party solution, larger drives can only be formatted to 128 GB in these models. There are three options:
  • Intech’s ATA Hi-Cap Support Driver
  • A PCI IDE card that supports big drives
  • A FireWire enclosure that supports big drives
• Power Mac G4 (AGP): Single channel SCSI cards may interfere with wake from sleep, Apple Knowledge Base, 2002.07.22. Computer may incorrectly assume card supports power down mode and not wake properly from sleep under OS 8.6.

https://lowendmac.com/1999/power-mac-g4-sawtooth/

And not sure on this, but it may also need to be sATA 1 compatible & those don't always check te SATA compatibility in the right order to work.

You could always attach an adapter like this to the back of the 2.5" drive and plug the ribbon and power cables into the back of it. A 3.5" hard drive requires both 12 volts and 5 volts, whereas a 2.5" drive only requires 5 volts:

Of those ebay listings that you provided, the representative photo of the used SSD indicates rough handling, as if it had been tossed into a box of computer parts. I'd have concerns about functional damage. The seller who has a "new" one listed indicates that 19 have been sold, but has no specific feedback for any of those 19 sales, if you search his feedback and use that exact item name. Were the buyers dissatisfied? Incidentally, when you post an ebay link, you can omit everything beginning with the ? and that follows it. It's the same with Amazon. Those hyper-extended links contain UTM data that's not necessary to include.

This project started with you wanting to use something that you already had, to replace an annoyingly noisy old hard drive. Noisy drives are causes by worn bearings from too many hours of ON-time. Production of mechanical hard drives improved as capacities increased. Years ago, I upgraded an iMac with an 80 GB IDE drive and the sound of the motor spinning the platter was barely audible. Replacing your existing hard drive with a "new-old-stock" 3.5" IDE drive would make a big difference, compared to the original. The problem with buying an older drive that's still "new-in-box" concerns how and where it was stored over the years since its manufacture. If kept in a non-climate-controlled environment, it could have problems. So, maybe you should continue trying to find a new SSD replacement, with the possible use of an adapter as shown.

Oh, sorry about that. I think the OS version is your problem. The Mac OS ROM files for OS 9.x.x predate the introduction of SATA buses and drives in Apple computers. A bootable PCI controller card must be firmware-based and not driver-based, because driver(s) in the Extensions folder of the boot drive are read after the startup process has begun. If the technology is unrecognized because the G4 can't make heads or tails of the firmware code on the controller card, it can't function properly. That's likely why the SATA controller card I linked isn't compatible with OS 9.x. The StarTech adapter doesn't have the necessary code for booting your 1999/2000 Sawtooth G4 via the IDE bus, even if it can successfully convert the hardware interface in a more modern computer. The USB-to-SATA adapter is a simple electronic adapter, so that's why you could connect the SATA drive and clone the boot drive to it.

Just for the purpose of testing recognition on the bus (even though the drive can't be bootable when the adapter isn't set to Master), did you try connecting the SATA drive to the middle ribbon cable connector and set the adapter's jumper to Slave? Depending on the manufacturer, the original IDE drive at the end of the cable may need to be reconfigured as "Master with Slave Present" (as opposed to Master/Single).

Unlike SATA, the older IDE technology was long-recognized and fully-compatible with OS 9.x and 10.x. I installed a Sonnet Tempo 133 Ultra-ATA (PCI) controller card in my oldest B&W G3, as the workaround for the problematic IDE controller chip on the 1st revision motherboards. It worked out very well and was worth the $99 MSRP. Today, seeing used ones listed on ebay for several times that amount leaves you wondering who'd pay that much.

Great suggestion & find! :)👍

I think you'll need something like this...

https://www.ebay.com/itm/353618597700?

The issue with the great IDE SSDs you found are that they're 2.5" drives & the Sawtooth's IDE connector is 3.5" ! :)