ADATA calls its repair program the Online Recovery Tool. You can read its launch announcement in HEXUS in November 2011.
Recovery software reads raw sectors for file signatures and directory records left after a deletion or quick format. It writes nothing to the ADATA drive and saves files to another disk. You can scan a stick that Windows refuses to open.

On ADATA's official support page, enter the drive's model and serial number. The site checks whether your model is supported before offering a small executable. Download it to run the repair locally against the connected stick. Forum users have reported problems with the lookup form for years.

The announcement lists three failure states: Windows cannot write to the drive, cannot format it, or detects it but cannot read it.

The drive can report 0 bytes of capacity and 0 bytes free together. In r/datarecovery threads, users describe sticks that were used and ejected normally, then came back RAW.
An interrupted write can leave file system metadata partly written, so Windows refuses to mount it. Your JPEGs remain in their sectors, but Windows has lost the index.
Do not click Format disk. Scan and save your files first. You can format the drive once they are safe. If problems persist after a clean format, try the vendor ADATA flash drive repair tool or check for controller failure.

Open Command Prompt as administrator and run diskpart. Replace 2 with your ADATA stick's disk number. Check it carefully: selecting the wrong disk risks wiping another drive.
diskpartlist diskselect disk 2
attributes disk clear readonly

If the attribute clears and the drive accepts writes, the read-only flag was the problem.
If diskpart reports success but the drive stays read-only, watch for these symptoms reported on data recovery forums: copied files vanish after reinserting the stick, deleted files return, or a successful Windows format changes nothing. A format that does not stick indicates that the controller has entered protective read-only mode. Copy everything you can still read and retire the stick.

If the drive appears in Disk Management without a letter, assigning one may make it accessible again.
In Device Manager, a warning triangle with "Windows has stopped this device because it has reported problems. Code 43" means the controller reported a fault and Windows dropped the device. An ADATA owner reported that message in Microsoft's Q&A. The official advice is generic driver troubleshooting, with no ADATA-specific fix. Try uninstalling the device and rescanning once; repeating it gives the same result.

Some ADATA UV128 sticks stopped being recognized in Windows 10 while still working under Windows 7, which points to driver enumeration. If your drive mounts on a Linux live USB, you have a route to the files.

After an accidental deletion, unplug the stick and leave it alone until you have a scanner ready on your PC.
JPEG, PNG and most camera formats have recognizable headers. SoftOrbits Flash Drive Recovery can use them to find photos even when the directory entry is gone.
A quick format resets file system structures while leaving data blocks and their headers in place. A full format is different; you cannot expect the same recovery result. The same applies to microSD card recovery software, since the media behaves the same way.

Searching for "ADATA UFD Recovery Tool P0909" may lead you to a separate firmware download, but the official channel is the Online Recovery Tool on ADATA's support site. Downloads on file-hosting sites carrying chip-vendor names are unsigned, come from unknown sources and target specific controllers. They can brick a working drive.

An AnandTech forum thread on the ADATA repair program reports that the engraved serial exceeds the form's accepted length. The form truncates it and finds no match. ADATA's support page does not document this. If the shortened number is still rejected, your model is outside the supported list.
For other brands, the order is the same: save files before firmware repair when you repair a SanDisk USB flash drive or use a Kingston USB recovery tool.

The controller translates file requests into commands the NAND chips understand. Every program, including ours, depends on it responding. You can check for hardware symptoms in an afternoon: repeated disconnections, errors that follow the drive across PCs, and "F:\ The directory name is invalid" returning after every fix.

The published free limits below come from the linked pages; they are not a ranking.