Data Centre Rack Power Connector options
In the US:


A 120V plug has Line, Neutral and optionally Earth.
A 240V Single-phase plug has Line L1, Line L2 plus Earth, or Neutral (3-wire systems), or both Earth and Neutral (4-wire system). I recommend the L14-30 (4-wire) type for the most flexibility, though L6-30 (3-wire, with Earth) is ok.
A popular option for data centers is 208 3-phase, delivered as 3 legs of 120V to neutral. Pairs of legs can be used for 208V.


Here’s a link below showing the lineup of NEMA types: https://www.lockingpowercords.com/topic/13-nema-locking-chart.aspx

And a discussion of using 208 3-phase power for the data center: https://www.raritan.com/blog/detail/3-phase-pdu-208v-60a-50a-power-strips-rack-pdus

As for 120 or 240v compatibility of specific US IT gear, you need to check with the vendor. Generally they do use universal AC power supplies, but there may be exceptions. The gear itself will usually have the ‘kettle cord’ IEC plug, and will use a specific cord to adapt to the wall plug in use.