If they are USB they are not always the same. Output DC 4.2v 420mA is what you want (which you can find on a label of the flat part where you screw in the battery). The 4.2v 420mA one is the most common and you can use it on just about every style of eGo or clone that there is. For example I had a KGO to start with and I use the KGO charger on my eGo Twists. I have heard of a straight to usb charger that used 5v 500mA output.
The output is very important. If you were to put a 5v output on a 4.2v battery (which most lithium ion
batteries are) it will 100% of the time cause the battery to vent and possibly cause a fire. The overcharge safety circuit doesn't protect against the wrong voltage charger. I learned about this after I saw a guy posting pictures of what had happened when he used the wrong output charger and he was very lucky it didn't damage anything else (he was charging it with a work computer!).
For more detailed answers to this and all questions
vape, please refer to the link in my signature to The Vaper's Handbook.