How do I restore windows back to their original screen when re-connecting external monitor?

Win Redock has worked best for me. Redock is automatic - saves and restores windows without any intervention. Magic! Its open source too!

I have, in the past, used an Autohotkey tool called Windowpad for this. Apparently this has now been replaced with a new, enhanced version called WindowPadX. Scroll down to see the readme. Full documentation is here.

This was crucial to me on multiple monitors. I loved to be able to easily switch a window between the two.

You can set hotkeys for the following (from the readme):

Possible actions to be configured on hotkeys

Window actions

Multi-Monitor

WPXA_MoveWindowToMonitor: Move window between screens, preserving relative position and size.

WPXA_MinimizeWindowsOnMonitor: Minimize all windows on the given Screen

WPXA_GatherWindowsOnMonitor: "Gather" windows on a specific screen.

WPXA_FillVirtualScreen: Expand the window to fill the virtual screen (all monitors).

General

WPXA_MaximizeToggle: Maximize or restore the window.

WPXA_TopToggle: Toogles "AlwaysOnTop" for given window

WPXA_RollToggle: Toggles "Roll/Unroll" for given window WPXA_Move: move and resize window based on a "pad" concept.

WPXA_TileLast2Windows: Tile active and last window

Multi-Monitor Mouse actions

WPXA_MoveMouseToMonitor: Moves mouse to center of given monitor

WPXA_ClipCursorToCurrentMonitorToggle: Toogles clipping mouse to current monitor

WPXA_ClipCursorToMonitor: Clips (Restricts) mouse to given monitor

General Mouse actions

WPXA_MouseLocator: Easy find the mouse