The PanelView Plus that you currently have and the PanelView Plus 6 consist of two separate components: the display module and the logic module. The display module is the physical touchscreen that you interact with. The logic module is the processor attached to the back of the display module, which stores the user program and has the power supply and communication ports.
Two separate items, both of which can be ordered separately. However, you can also order a complete unit, which will come with both the display module
and the logic module, and has a different part number again. It can be a little confusing when one vendor offers you a separate logic module and display module, and the other offers you a complete unit - they may both be selling you exactly the same thing, but with different part numbers!
Here's what you currently have:
2711P-RDT12C: PanelView Plus 1250 Display Module
2711P-RP1: Panelview Plus Logic Module, 64MB, 24VDC power supply
If ordered as a complete unit, the part number would be 2711P-T12C20D1
Now, those particular models have been superseded (a couple of times, in fact), and are no longer available. What your vendors have quoted you is the PanelView Plus
6 series, which is physically identical to the PanelView Plus series you currently have. It has some software differences, but it is completely backwards compatible - that is, the Panelview Plus 6 will happily run programs developed for your older Panelview Plus. So all you need to do is work out the equivalent Panelview Plus 6 part number.
That brings me to the most important question: what is wrong with your existing HMI? If the screen is cracked or damaged, but otherwise it is still working, you may be able to just replace the display module and keep the existing logic module. If the screen itself is good, but the logic module won't load the program or something similar, you may be able to just replace the logic module and keep the existing display module. Or, perhaps you aren't sure of the problem, or the whole thing has sustained damage and failed, in which case you could either buy a separate display module and logic module, or buy a complete unit.
Panelview Plus 6 1250 Display Module: 2711P-RDT12C
Panelview Plus 6 1250 Logic Module: 2711P-RP8D
Panelview Plus 6 1250 Complete Unit: 2711P-T12C4D8
Basically, your first vendor has offered you only the logic module. This is a viable solution only if your display module is still functioning correctly
and is compatible with the PanelView Plus 6 logic modules.
Rockwell Automation Knowledgebase Article 115612 (access: everyone) specifies which display modules are compatible with the newer Panelview Plus 6 logic modules. Unfortunately, your logic module is not...
The following display modules have 5-wire touch screen, and therefore will not work with the PanelView Plus 6:
2711P-RDT7C / Series A
2711P-RDB7C / Series A
2711P-RDT12C / Series A
2711P-RDB12C / Series A
2711P-RDB12C / Series B revision A
So, unfortunately, the first vendor has offered you an incomplete solution that will not work for you.
The second vendor has offered you a complete replacement - their part number represents a complete unit incorporating both a display module and a logic module. This product will run your application correctly.