And, I think, at last, I figured out how to do it (it rather puzzled me when you got two different screenshots ...). Turns out there are two ways you can tell Windows to align keyboard shortcuts in the drop-down menu.
The first (and probably the most standard) way is to insert a tab character ( \t ) in the line corresponding to the menu text. This gives the bottom example shown in your original question, the one where all identifiers are left aligned and slightly overhanging. This is the standard in almost all Microsoft applications, and the only option that I knew existed up to a few minutes ago.
Example resource string: &Print…\tCtrl+P
The second way is to replace this escape sequence \t with \a in the resource string (which, yes, oddly enough, a warning call usually indicates). This causes Windows to align all the shortcut keys in the menu, creating the example shown in the first screenshot. This creates a menu that uses the screen space more efficiently (it is smaller), but this happens by carefully aligning each of the shortcut key sequences down their left margins, which in my opinion makes reading easier.
Example resource string: &Print…\aCtrl+P
So, if you want your menus to look like the second example in your original question (yes, I vaguely sorted my samples back. Sorry), you need to delimit the shortcut key sequence with a tab character ( \t ) in the resource file containing text lines menu item.
It's strange that you claim to use .NET WinForms, which handles all this automatically (saving you the pain of bothering with resource files). I know that it inserts tabs, and all the menus I've ever seen, they look like your second example.
The best thing you need to do is switch your menu to the old MainMenu control included in an earlier version of the .NET Framework. (To do this, you probably have to right-click on the toolbar and add the control manually - it is not present by default in later versions of Visual Studio.) This will make sure that you see the alignment behavior that you expect in compliance with all standard Windows applications, such as Notepad. It also creates menus that look like the operating system’s own menu (in Vista and 7, they are colored blue), rather than the amateur looking menu owners created by the MenuStrip controller, which do not fully comply with the modern requirements of the Windows version.
Microsoft's official documentation confirms that MainMenu control is still supported for future use, so there is no reason to be afraid to use it in your applications. I highly recommend everyone to use this instead:
Despite the fact that MenuStrip replaces and adds functionality to the management of previous versions of MainMenu, MainMenu is retained both for backward compatibility and for future use if you choose.