You can't combine more than one discount, but if indeed one is a discount and the other is a form of payment then you can. As FlyingNone recommends you can bring them in, but depending on who you get if you say "can I do this" the answer will probably be no. What does it say on the back of both? If you can type in just the applicable info we can probably arm you a little better. Or maybe if you can tell us how you got the $150 dollar one we can help. CS gives out $150 discount certs so my inclination is it is a discount, but that is just a gut feeling without knowing what it is from.