There's mixed opinions on this. On one hand, the concept of dynamic effort work for powerlifts increasing your strength is a staple of Louie Simmons and Westside Barbell templates. Most of them will say it works. On the other hand, there is a camp of lifters, including Boris Sheiko the Russian IPF coach, who say that increasing speed with submaximal weights will not carryover to max strength, and if it does work it is only because the submaximal loading allows the body to recover from heavy max work and there are better ways to program this (i.e., 5 sets of 3 with 80%, rather than 8 sets of 3 with 55%). I've never done hardly any speed work, so I can't compare them from personal experience. Try it and see if it works. There seems to be a trend of guys doing "speed work" at higher %'s, 70-80, which would really make it SE rather than DE. So at least in internet forum lore, the latter method seems to be more popular now.