I have 2 MBPs:
1. Personal MBP 2011 15" (with 85W magsafe)
2. Work MBP Retina 2013 13" (with 60W magsafe 2)
So can I use my 85" magsafe for my 13" retina using this converter without any power issues?
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Apple themselves states that it is safe and okay to use a higher power cord on a laptop even if it only requires a lower power one: http://support.apple.com/kb/HT2346
The power requirement for your computer really is just a "minimum" power requirement. If you can even call it that. Because they'll actually charge even on lower powered cords, but it will be slower and it's not recommended. MacBooks can officially (meaning Apple supports it) use cords that supply more power than the standard provided by the default cord. The computer will actually only pull what it needs from the cord, it's not as if the cord will force as much power as it's rated for into your computer.
As far as the adapter, there shouldn't be any issues with it. Apple states that it's for using a MagSafe cord with a MagSafe 2 MacBook. Which at least implies that it supports all MagSafe cords, and all their different power outputs. And there's not really a reason I can think of why it shouldn't anyways. There is an 85W MagSafe 2 cord, and I doubt Apple would make an adapter that wouldn't work for those computers that require it.