if its a TRUE 5v passthrough then you should be getting 5v vapor which is substantially more than 3.7, another tip would be to plug your passthrough in for an hour, then unplug it and try to
vape. If you CAN vape with it unplugged than it most likely has a battery that runs at 3.7 and just charges on the usb connection. Basically you want a direct line to your 5v usb port.