The amperage available determines how long it takes for the phone to charge. All current cellphones require ~5 Volts, which is what all chargers supply. If you pay more than $5 for a plug-in car charger, you're being ripped off, unless you want to walk in riand walk out right now with a charger. There are plenty of good ones on eBay and Amazon for a few bucks. (I've had one in each car for a couple of years, and I think about the ash tray more than I have to think about the chargers - they just work. I think one was about $1.50 from China, the other was about $2 or $3 from Amazon.)
If you have a Samsung phone, and you want it to charge at the rate it charges when using the wall charger, you'll have to buy a Samsung charger - they have a "special circuit" (actually 2 shorted pins) to tell the phone to charge ar a higher rate. But if your phone does okay charging from the computer, any charger will do. (A Samsung charger is about $35 - $1.50 for the charger and $33.50 for a half inch of wire shorting 2 pins in the plug.)