The following information should be accurate for all PSP models with a TV output. This assumes you are using the component cables.
The PSP follows the Rec.601 video standard. As such make sure you are capturing in a colour domain of YUV(601) Limited. Your Horizontal size will always be 858.
The PSP has multiple video modes. It is capable of outputting 240p, 480i and 480p. In each resolution it has a width of 720px. The height caries on the resolution. When playing PSP games the game is in a black border. This is due to the fact that the native resolution of the PSP is 480x272. You cannot scale it by an integer and have it fit in the 720x480 video frame. If you are capturing it would be ideal to edit out the border in post.
The PSP is also capable of playing PSX/PSONE games. This leads to the 240p output of the PSP. The resolution when playing these games is 720x240. You will have to point/nearest neighbour scale the capture to 720x480 as to not have a very wide video. The PSP is also capable of switching into 480i mode while playing PSX/PSONE games. This means that in games that change resolutions, your capture device or video processor will drop the signal as if you were playing on a PSX/PSONE or PS2. One thing to note is that it seems the PSP seems to cut off the top 10 pixels of the video when playing these games. This may be an issue if the game uses the full 240 pixel height instead of 224. Refer to the POPS section on the PSX page for more information.
Visual Comparison
480i vs 480p
It seems that the 480i output is cleaner than 480p but more testing is required to be 100% sure.