Hi!

I want to buy a portable MP3 player (not IPod), but it requires
a "high power" USB port on a computer to charge it.

"High power" is an Apple-esque description of a USB port that is part
of a *powered* USB hub or built in to a computer (a "root port").

Basically, as long as you plug the MP3 player into a USB hub with its
own power supply or directly into the computer, it will be fine.

If you were to plug it into a "passive" hub such as that found in a
monitor or keyboard with USB ports, there might be a problem with
insufficient power being available.

I am a service technician, and I thought about using one of my
regulated power supplies. *You can set voltage and current.

Be very aware of polarity, and make sure the power supply's regulation
is as good as you think it is, especially with light loads. The
designers of your MP3 player may have assumed that its power input
would never be mistakenly reversed or set to a voltage that was just
too high.

You are looking for 5 volts DC at a maximum of 500mA.

William