Hi jeremykayp - I think you've got your clues mixed up -
18d Covering it up, disposing of regular income - Stipend - 'it' (up, in) 'spend'
16d (the pattern you show) - A rock overturned with what, from the sound of it, is a lot of power - Megawatt - 'a gem' (over) + 'watt' (sounds like "what")