What is the best model for hiring suppliers that best match with Scrum?

If value is emergent and evidenced Sprint by Sprint, why not approach suppliers with a view towards adopting a contract model along those lines?

Is it so bad that your IT suppliers are on a defined scope model? If you understand a body of work, you can potentially send that work to a supplier and that supplier becomes a black box, interacting with you on a cadence and terms specified up-front. However, by simply being agile yourself, you are reducing the risks of interacting with the supplier - you are capable of accepting a delivery and then working with it within one or two iterations and you are also capable of adjusting your plans should a delivery be late.

The best case scenario is if your supplier is also iterative and incremental, since this would reduce their risk and your risk. However, by you being iterative and incremental, you are already reducing your risk. So as long as the interactions from your side are specified and acceptable and the contracts specify conditions for action taken on failure and terms for renegotiation, does it matter if your supplier chooses a riskier path for themselves?

Hi,

When I say "defined scope model" I mean closed scope where my schedule and budget are linked with my scope contracted.

Here, whenever I have a change request, my budget and schedule are impacted (in 90% of the cases) and my team are not able to lead with those changes in a fast and costless way.

Just because we manage scope and not the business needs looking after to its experience.

Cannot readequate the projects with new requirements because suppliers support themselves on the contract signed.

"suppliers support themselves on the contract signed" - this is precisely what contracts are for. If you feel like more agile, we can only support you and suggest re-discussing the approach with suppliers, and then contracts.