How can I keep objects from resizing when replacing contents?

I make mockups using this method ALL the time. I have only gotten Replace Contents / Relink to File to work with a Smart Object IF the images are the exact same pixel dimension AND the exact same resolution as well. I wish this were different. Sometimes you don't want to take the time to homogenize all your images. 

Check the file to be replaced to ensure that it has the same Resolution Pixel Per Inch as the one that is already placed. Double click on the Smart Object layer to edit it and verify the Resolution.

exactly same issues i have been facing. I need help with this

So, I know this thread is old, but I figured out what I was doing wrong.  I'm creating a tempate for my girlfriends candles to easily produce product photos with different labels, and I was having this exact issue.  It's important NOT to resize your image unitl after you've made it a smart object.  I was dragging and dropping the image, resizing it as that's the very first thing you do, and then turning it into a smart object.  This would cause the image to resize when replacing contents.  You should drag and drop your image and just hit enter without resizing.  Then convert to a smart object and apply free transform to resize to your needs.  Then you can just right click on the layer and pick replace contents, and it should keep the size you've applied.  Doing it in this order solved my issues. 

I think i worked this out, if you are using smart objects make sure the layer you are replacing is a background layer with the padlock icon shown. This seems to lock the scaling if you replace the file. If your file is not keeping the same transform settings when you replace it with a new one go into the smart object, click your layer, go to Layer > New > Background From Layer. This fixed the issue for me.

I realise this post is old but I wanted to add my solution if it helps anyone.  I'm no expert but I've had the same issue with smart objects resizing when I replace the contents and I've just found out why. I have been opening up my replacement object in Photoshop, converting to a smart object, resizing to match the dimensions of my original smart object and then exporting contents to a .psb file. When I go to replace contents of the original smart object with my new .psb file it annoyingly resizes. I have the resize box unticked in Preferences I hasten to add. BUT.... I have just discovered that if I double click inside the ORIGINAL Smart Object thumbnail to open it up in a separate document, the dimensions are totally different to the dimensions it shows from the transform panel in my original document.  So, using the newly found dimensions, I apply these to my new replacement smart object before exporting and now when I replace, it is the correct size!  Like I say, I'm self-taught so am certainly no expert but I'm just happy I've figured out a way to do this.

Umm, no. Replacement object DOES NOT pick-up attributes of replaced object. Not in CC anyway.

I don't think this question was properly answered.

In order to have a smart object maintain the scaled size when you replace it with new content, you must place the ORIGINAL object using File > Place Linked. If you introduce the original file to your artboard any other way ... like dragging it over & converting it to a smart object, then the 'Relink to File' and 'Replace Contents' commands won't work as you would expect. It'll replace the object, sure, but it will maintain the size of the object you're replacing with rather than maintaining the scaling effects you've applied to the orignal.

I am having the same problem.  Mine actually WAS working where the images would import and be formatted to same size as the original image I was replacing but now they are coming in bigger.  I guess I must have changed a setting because now the images being imported are too big and are not conforming to the size of the original image.  I have even tried redoing this with files that were successful before but they have now changed and are too big.  I believe there must be a setting that will allow for this, but I don't know what it is!  I wish I could figure out what happened!