If the Smart Y is Charles, it will ONLY work if both legs of 50 are in phase. The Hubbell will work on one leg, and if the phasing is wrong on the second leg, it will only give you the 50, not 100. So if you're low on volts, you're losing available amps to make up voltage, amps being converted to volts. Compounded if your load is lopsided to one leg. Made even worse if the Smart Y is actually limiting you to 50 amps. If the Smart Y is Hubbell, is the light yellow or green once you've heard the click of engaging?