Usually there is no difference, the "90-10" is just a misnomer. There are a few concepts in play here:
1) An 80-10-10 is most often used to avoid PMI. The way this is accomplished is by keeping the loan-to-value (LTV) on the first mortgage at 80% or below. So, you wouldn't do a "90-10" because that would put you back in the mortgage insurance situation.
2) The idea of any "piggyback" loan starts at trying to allow the buyer to make less than a 20% down payment. A piggyback allows a down payment less than 20% and no PMI.
3) A true 90-10, if it exists, would mean 100% total financing. We just don't see that much anymore except for VA loans.
4) More often than not, if someone says 90-10, what they mean is a 10% down payment with some sort of 90% financing in front of it.
Here in California in 2017 we can do 80/10/10 loans even with jumbo programs and up to a price point of $1.9MM. The rates and terms are very much in line with 20% down payment programs. If you have questions about making less than a 20% down payment I'm happy to help.