Mixing number chapters with letter appendices?

I am trying to create a document that follows 

1

1.1

1.1.1

2

2.1

2.1.1

H:Module: <$chapnum>< =0>< =0>< =0>< =0>< =0> (Using this number format )

for the main content in the book (This is working and works exactly as needed)

Then for appendices, I would like to use letters for each appendix section 

A

B

C

I have it set to number as such

G:Appendix: <A+> -< =0>< =0>< =0>< =0>< =0> (mimics the chapter numbering)

With this each new appendix section starts at A instead of A, B, C etc. 

How can I manipulate the format so that it numbers as desired? The overall numbering/ TOC would follow:

Ch 1, Ch2,...Ch 10, Appendix A, Appendix B, Appendix C

Thank you for any assistance