Why do Liberals support trickle up?

I think liberals are generally skeptical of "trickle down" economics because they are doubtful that much money actually trickles down from the rich to the middle class. However, they point out that with "trickle up" economics the poor and middle-class will use that money to make necessary purchases and that money will then trickle up to the corporations and the rich. There may be something to that but I don't pretend to be an expert in these things (and generally think anyone who does is lying) so I can't say for sure.