Third Party chargers are not supported by VholdR themselves and may void your warranty.

Off of that, I have used any number of wall chargers, car chargers, with my vholdr & contour HD's and they have charged the unit fine.

(I am not that technical, and don't know if those specs differ from what the USB terminal of a desktop normally outputs.)
All usb put out 5v dc... computer usb port are supposed to be able to supply 500ma.
If your charger puts out 1a, it will charge faster provided the cell can take that level of charge.
I use my Moto Razr charger (1a) for a lot of my usb units, its just easier to carry one charger.