PSU
The PSU file format is an archive format used by PS2 save data management tools like uLaunchELF and mymcplus.
Usage
Obtaining a PSU file
From an actual PS2
By running uLaunchELF on an actual PS2, one can export PSU files from the PS2 Memory Card to USB or network.
From a PS2 emulator
PCSX2 stores the PS2 savedata in a virtual memory card file whose extension is .mcd. Each per-game savedata contained in the MCD file can be extracted to a PSU file by using mymcplus tool for example.
Extracting a PSU file
The best way to extract a PSU file would be to use pypsu by McCaulay if it was not bugged (for example on Jak X: "[-] month must be in 1..12", and on games that have a filename identical as the folder name, cannot export that file).
So the current workaround is to convert PSU to another savedata format.
For example, you can use
In the past there was a tool named psutools (link requires registration)