Supply chains are literally chains of suppliers, e.g. vendors. Your 'simplest electronic product' could absolutely be constrained by whom you choose to work with.

If your vendor locks you into buying from a certain source, and their vendor requires the same, and so on up the chain, how would you describe that dynamic to differentiate from a single vendor being the point of restriction?

To your point that the phrase didn't exist, here are three supply-chain oriented papers that directly reference the phrase: This paper is exploring the social dynamics of buyers and sellers:

Lock-in situations in supply chains: A social exchange theoretic study of sourcing arrangements

Specifically, we believe that the examination of lock-in situations between a manufacturer and its supplier, i.e., instances where for all intent and purposes, one party is heavily dependent upon the other party, with few alternatives, under social exchange theory, can provide new insights into controlled self-interest behaviors (e.g., strategies) in on-going supply chain relationships.

This paper is about supply chains in plastic management, but the phrase is here:

Business models and sustainable plastic management: A systematic review of the literature

Barriers frequently mentioned were high costs, complexity of new systems, supply chain lock-in and low customer buy-in.

And here's a paper about optimizing your supply chain where it is referenced as something to avoid:

Orchestrating cradle-to-cradle innovation across the value chain

This one even has a handy definition:

Supply chain lock-in:

Contracts and strong dependencies with suppliers not supporting circularity (e.g., either due to non-willingness or lock-in in production facilities optimized for linear concepts). 

I suppose if you would like to be super extra pendantic Wikipedia does have you covered with "Collective Monopolistic Vendor Lock-in".