Most of Smiths homers have been in garbage time in blow out losses. I can’t recall one that was significant.
For fun, I pulled up the the play log for the games with his 10 homers. Thankfully, it's easier than doing this for Aaron Judge or Matt Olson
I'll post the score and situation, as well as the change in win probability (I'll give the % change). Right away, your recollection is spot on for homer #1 and #10.
#1 - 4/29, 9th inning, 1 out, Pirates lead 16-0. Solo. Win Prob %=0%
#2 - 6/11, 6th inning, 1 out, Nats lead 4-2. 2 runs, change in win probability=13.1%
#3 - 6/26, 2nd inning, 2 outs, Mariners lead 1-0. Solo. 12%
#4 - 7/1, 2nd inning, 1 out. 0-0 with the Phillies. Solo. 10.6%
#5 - 7/9, 5th inning, no out. 0-0 with the Rangers. Solo. 14.1%
#6 - 8/23, 9th inning, 2 out, 9-0 NYY. Solo. 0%
#7 - 9/2, 5th inning, 1 out, 9-1 Marlins. Solo. 0.8% (from 1.1% to 1.9%).
#8 - 9/11, 6tb inning, 1 out, 4-1 Nats leading pirates. Solo. 6%.
#9 - 9/13, 6th inning, 0 out, 7-3 Pirates. 2 runs. 9.8%.
#10 - 9/18, 9th inning, 2 out, 6-0 White Sox. Solo. 0.1%.
Remarkable collection of no-impact homers. 4 out of 10 with less than 1% impact. Also, as a general matter, his power surge is largely in September, when the Nats are playing out the string rather poorly. In fairness, 4 are also in the stretch from 6/24 - the end of August when the Nats were well above .500.
