DS dumps are .nds files. DS images can be much larger than the IPS offset range, so xdelta is a practical format for many translation releases. A translation or a menu overhaul is shipped as xdelta so the download is the difference, not a second copy of a 128 MB card. The browser can apply that xdelta when the tab can hold both files. I will not pretend there is a published byte cap. People do hit memory pressure, and the honest fallback is Delta Patcher or xdelta3 on the desktop, which stream instead of keeping the whole window in a tab.
The other DS-specific failure is secondary compression inside the xdelta, not a bad dump. If the message names a secondary decompressor, the patch was written with xdelta3's default extra compressor. The build pinned on this site decodes DJW and LZMA. An older copy of the same engine does not. I would update the tool before I re-dump the cart. Checksums still matter: a European card and a US card are different .nds files, and a trimmed or decrypted dump may not match the author's hash either.
3DS is not this console. A .3ds or .cia is a different container, often larger, and many mods are LayeredFS folders rather than a single patch. I mention it only so a DS search does not land on the wrong guide. Emulators after a successful DS patch are melonDS and DeSmuME on desktop, or a handheld core that accepts a plain .nds. The patcher stops at the file.
RUP patches with the NINJA2 header also show up in DS tooling. They apply in the same browser engine. If your file is .xdelta, stay with the xdelta format page for the compression details and come back here for the size warning. Related reading: xdelta, the secondary decompressor error, and Delta Patcher.
