scout has 12 servos and each can draw upwards of 2A, so 10A isn’t so much but it isn’t bad either. You are running it tethered though so consider how long your wires are, what wire size, and how solid the connections are on each end. you could be getting short voltage drops when you have large current demands that would not be readily apparent with a meter. this would not exist with a battery pack attached to the scout.
something to try as a test if you can would be to place a large electrolytic capacitor, several thousand micro-farads, at the point the wires from the power supply enter the scout. keep the connections as short as can be allowed. this way if there are current spikes causing a problem the capacitor can supply the current.