If you’re still looking for a Dark Alex release of 5.50 custom firmware tough luck. The good news is that members of team M33 has released their version of 5.50 much like what they did with 5.03 (5.03 MHU A.K.A. Custom Firmware Enabler). Do note that this custom firmware is for PSP-1000 / non-TA088v3 PSP-2000’s.

Important: DO NOT attempt to install this on PSP-3000 / PSP-2000 TA088v3. YOU WILL BRICK YOUR PSP IF YOU DO.
 
Requirements:

• PSP Phat or PSP Slim with 3.52 M33 or higher. If you don’t have custom firmware yet, READ: Convert your PSP to custom firmware.
• PSP battery that’s at least 78% full
• Download: 5.50 MHU | 5.50 MHU
• Download: 550.PBP | 550.PBP
• Disable ALL plugins.
• Back up your save files (so that if they get corrupted, you still have backups)

How to install 5.50 MHU CFW on your PSP:

• Extract the MHU files to your computer.
• Copy the PSP folder to your PSP’s memory stick. (Yes, just drag the whole folder there)
• Extract the 550.pbp files to your computer.  Rename it (the file’s name is EBOOT.pbp) to SCE.pbp.  This is important!
• Copy the SCE.pbp to X:PSP\GAME\UPDATE folder
• Disconnect the PSP from USB.
• Run 5.50 UPDATE from under Game on your PSP’s XMB
• After all process is complete, press X. Your PSP will reboot.
• Congratulations, you’ve just installed 5.50 MHU

Important Notes:

• Always use the M33 driver. The SonyNP9660 driver doesn’t work.
• Update network doesn’t work. It will get the official firmware so don’t use it.

What do I get with Custom firmware 5.50 MHU?

• All functions of the official 5.50 firmware
  • The [Information Board] has been added under [PlayStation Network]

  PS3 owners are already familiar with this feature. It displays news and updates from SCEE in the upper right corner of the screen. You can now obtain information about the games ahead of the new content available on the Playstation Store, and other news from your PSP even if you are connected to WiFi.

  • Support for Internet security service provided by Trend Micro has been added to [Internet Browser]

  End Micro Web Security: use technology to block access to malicious sites that can steal personal information and confidential -
  Trend Micro Kid’s Safety: You can block access to websites with inappropriate content.

  • An icon for built-in Internet Search has been added to the menu bar of your browser

  Instead of having to point your browser to Google then search, you can do your searches directly on your XMB.

  • Option to search for the game title on Google.

  By selecting the icon of the game and then pressing triangle and selecting running Internet Search, you get to search for sites using the name of the game.

  • It is now possible to see an additional level of hierarchy under [Photo] [Music] and [Video]
• Launch of UMDs to ISOs to CSOs and demos require firmware 5.02 or below
• Launch homebrews
• Launch of PS1 games (converted to PSP)
• Access to Recovery mode (adjusts the processor speed of the PSP, FLASH access, use plug-ins etc.).