Chinese Power Supply 180-260v on US 220v Electric
There are several issues here. But the good news is, you erred on the side of overdesign, so it'll be easy to put it right, and you'll wind up with a fair bit of spare capacity.  For instance, running 6/3 was a great move.  It didn't add much cost and it gave you versatility you can put to good use. 

That power supply

The power supply is rated at 1300W output.  One aspect of its cheap Cheeseness and lack of UL listing is that it doesn't have a nameplate power rating, or the power it needs from the power grid. This differs from output rating by a) power supply efficiency, and b) power factor. Skipping the gory details, I'm going to SWAG-guess the nameplate at 1800 VA.  The numbers work out reasonably well if I do that. 

(feel free to google VA and how it differs from Watts). 

Aside from that "reality check", this will be a continuous load so we must do a derate of 125%.  That means we need to provision a circuit for 125% of 1800 VA, or 2250 VA. 


This is just within the 2400 VA capacity of a 120V/20A circuit.  You would need a step-up transformer, but this would supply correct neutral to the power supply.   
Two would just fit on a 240V/20A circuit (4800 VA)
only one would fit on a 240V/15A circuit (3600 VA). 


Your 60A circuit has 240V x 60A = 14,400 VA.  You won't have any trouble provisioning three 2250W loads on the circuit.  In fact, you could get six. 

Powering the units, and neutral

RedGrittyBrick points out a serious issue. These units are made to be connected to hot and neutral.  In USA 240V power, there's no neutral, it's hot and hot. The neutral on the power supply would need to be insulated to tolerate being 120V from ground, and it may not be.  If only the factory could advise you!   Regardless, here's how to fix it. 

They make "step-up, step-down" transformers.  You supply 120V at 20A (2400 VA) to the transformer.  It passes the neutral straight through (so that is satisfied). Then it doubles the voltage of the "hot" wire, giving you exactly the right thing: 240V and neutral. 

Supplying 120V is possible because you used /3 cable. 

Power distribution off 60A

You can't just hotwire all 3 power supplies to a 60A main, especially when they're cheap units. Putting a 1800W unit on a 14,400W circuit breaker is nearly worthless, because the trip point (14,400W) is so very much higher than the rating of the power supply (1800W).  You need more sensible breaker sizes. 

How to safely split up that 60A supply: 

PDU. Your first option to distribute power is a PDU, which is computer equipment made to sit on the bottom of a rack, take a fat power connection, and distribute it to individual servers in the rack, with sensible circuit protection.   However PDUs are expensive, and subpanels are cheap. 

A quality QO panel is about $45, a cheapie BR $22, breakers are $5 or $9 for 240V types.  

Subpanel.  Normally I recommend the biggest subpanel you can afford.  But in this case, there's no use for more than 8-13 spaces (it's rated current must be at least 60A).  And then, you fit breakers like this. 


If using step-up transformers, fit 3-6 120V/20A breakers (2400VA each). 
If using 240V, use three 20A breakers (4800 VA) and put up to 2 servers per circuit. 
Or using 240V, use 3-6 15A breakers (3600 VA) with 1 server per circuit. 




Note in the 120V example, you really have to watch breaker placement for the servers. Place the server breakers in pairs side by side, just like 2-pole breakers. Do not put the 6 server breakers in the top 3 rows. The aux circuit is for small loads like monitors, switches etc. 

Don't parallel.  Use three subpanels. 

Neutral and ground must be separated in the subpanel, so add an accessory ground bar ($5) and remove the green screw on the neutral bar to unground it.  This makes 120V available.