A little more information is needed if you don't mind.
The schematic that was drawn in the video is correct by the way.
First, do the fuses blow immediately when you apply power or only when you turn on the bed heat through the control board?
If you disconnect the SSR and its wiring (as shown above) and connect power to the plug receptacle and then turn it on, do the fuses still blow?
I ask that because from the photo it appears to me that you may have connected the output of the fuses in the receptacle across the switch portion.
If so, when you turn the switch on the fuses will be driving a dead short.
Here is how receptacles of the type supplied with these kits are supposed to be wired-
If you are using some other type of receptacle you will need to refer to its manufacturer's literature.
While unplugged from the AC source (obviously) put new fuses in without the heater connected, turn the switch on and test for a short from the line to the neutral blades of the socket.
Or from either line or neutral to the ground blade for that matter.
If any of them are shorted then something is wrong with your receptacle or the wiring on it for sure.
Is this a separate AC power entry module from the normal one?
Or if it is the regular one that was used for the printer, why don't you just get the power from the PSU's AC inlet connections?
That's what I did and have had no issues whatsoever doing so because the wires provided in the kit for the AC side are gross overkill for the current they are handling and you can easily put a wire on each side of the clamp screws.
What size of fuses are you using?
Are they appropriate for the new total load?
What is the rated wattage of the new bed heater?
I presume that you are running the correct line voltage for the new heater?
Finally, have you checked for shorts in the heater itself?
It must have a resistance typically in the range of 20-30 ohms (500-600 watt heater made for 120V operation) or 80-100 ohms (500-600 watt heater made for 240V operation).
Alternatively, are there any shorts from any of the heater wiring to any grounded surface?
How about from the SSR terminals to a grounded surface (very rare but not unheard of)?