xDai Chain validators are independent organizations. They joined this public service voluntarily. They protect the public value of xDai Chain by participation in consensus, governance, interoperability.
You can always find a list of validators using Validators dApp here. To connect the dApp to xDai Chain network you should switch the network to xDai Chain. xDai Chain is natively supported in Nifty Wallet or add a custom RPC to MetaMask (https://dai.poa.network , NetworkID 100)