Based on your financial expertise, provide your response or viewpoint on the given financial question or topic. The response format is open.

Transferring money from One business checking to another business checking
You should have separate files for each of the two businesses.  The business that transfers money out should "write check" in its QB file.  The business that receives money should "make deposit" in its QB file. (In QB you "write check" even when you make the payment by some other means like ACH.)  Neither business should have the bank accounts of the other explicitly represented.   On each side, you will also need to classify the payment as having originated from / gone to some other account - To know what's correct there, we'd need to know why your transferring the money in the first place and how you otherwise have your books established.  I think that's probably beyond the scope of what's on-topic / feasible here. Money into your business from your personal account is probably owner's equity, unless you have something else going on.  For example, on the S Corp you should be paying yourself a salary.  If you overpay by accident, then you might write a check back to the company from your personal account to correct the mistake.  That's not equity - It's probably a "negative expense" in some other account that tracks the salary payments.