Let me see if I got your question correctly:
When you say "
power supply has 16 pcie", do you meant to say that your power supply has cables with 2 PCIE connectors which are 6+2 pins (8pin) each like this:
If so, then,
yes. You can plug those two 8-pin (6+2pin) connectors on a graphics card having 6 and 8 pin sockets on it.
Simply plug the first 6+2pin (8pin) from the power supply to the 8pin socket of your graphics card. Then, plug the other 6pin (leaving the 2pin unattached) from the power supply to the 6pin socket of your graphics card. It should look like this: