This cable for the Sony Ericsson z550a does the job; it connects well to both the cell phone and PC USB port effortlessly.
The problem I have is the fact that the cable has trouble retracting!If you want to retract your cable, you pretty much have to hold the "retract" button and manually feed the cable back into the "cord chamber" (or whatever you call it). I think I would have been better off to purchase the non-retractable version.
The cable was shipped promptly, arriving three days after I ordered it, with no frills; you get the cable in a little zip-lock bag and a receipt of your order, packaged in bubble wrap in a large envelope.
If you're considering getting this cable (or any other sync cable for the Sony Ericsson z550), you'll need to know how to transfer files to/from the cell phone from your PC. Pictures, video, and audio files are easy to transfer, but there doesn't seem to be an easy way to transfer games or JAVA apps to the phone (I'm still researching this). This is not the cable's fault, but if you're looking to transfer apps and games to the phone, you need to consider such possible limitations.
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Retractable USB Cable for the Sony Ericsson z550a with Power Hot Sync and Charge capabilities - uses Gomadic TipExchange TechnologyProduct Description: Charge your mobile devices while synchronizing data with one cable custom designed to work with our TipExchange Technology that enables hundreds of mobile devices to work with the same cable (Tip Included). Cut loose the rest of those cords to make this cable the hub of your mobile workstation and enjoy a minimalist workspace anywhere you go.When your device is fully charged simply remove the device and custom tip and replace it with any of your other mobile accessories.In addition; this product; like all Gomadic products; is backed by a lifetime warranty.
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It was genuine Dell and ive been using it for a little over 3 weeks now. Awesome!
The accessories that I ordered arrived within a week and were packaged well.Everything is working great and I was very happy with my products.The price was very affordable compared to other pricing in the area that I live.I was very happy with my purchase.
Audio can be tricky.One setting can stop things.I got no audio out of this on Windows Vista 64.I couldn't find a model number that would allow me to google manufacturers information or usenet type information.
The Sony Ericsson P990i Retractable Power Hot Sync and Charge USB Data Cable works fine. No problem at all.
The 4 MB chip was a good price. 
Basically, I have told everything in the title already. The product is great. No installation needed, you just put it in USB-port and it starts working! Came fast. It is portable and fast. I am using it for about 4 months now. At least at this piont - no troubles.